The Bloom of Animosity
An original editorial by Joshua Bradshaw
One of the most difficult sibling relationships to analyze in the books published to date is that of Lily Potter and Petunia Dursley. We have very few direct quotes to go by due to the fact that as the books begin, Lily has already been killed and Petunia avoids talking about her sister except in the most extreme circumstances. First, let's take a look at what is said, and then we'll read between the lines to try to determine what is unsaid.
In Sorcerer's Stone / Philosopher's Stone we have:
(all page numbers are from the American versions)
On page 2, "Mrs. Potter was Mrs. Dursley's sister, but they hadn't met for several years." The setting here is the day after Lily's murder. From this we can gather, based on estimations of the time-line, that Lily and Petunia parted ways very soon after Lily graduated from Hogwarts.
Page 5, "she always got so upset at any mention of her sister."
Page 53, "Of course we knew! How could you not be, my dratted sister being what she was? Oh, she got a letter just like that and disappeared off to that - that school - and came home every vacation with her pockets full of frog spawn, turning teacups into rats. I was the only one who saw her for what she was - a freak! But for my mother and father, oh no, it was Lily this and Lily that, they were proud of having a witch in the family!"
And further down, "Then she met that Potter at school and they left and got married and had you, and of course I knew you'd be just the same, just as strange, just as - as - abnormal - and then, if you please, she went and got herself blown up and we got landed with you!"
This is the sum total of all insight we get from the first book. While other mentions of her attitude are made, they aren't clear enough to determine if this is just Harry's interpretation of her mood, her attitude toward Harry, or her attitude toward her deceased sister. To find more information we must skip all the intermediate books and go straight to Order of the Phoenix when she becomes outraged enough again to speak about her sister.
On page 32, "I heard - that awful boy - telling her about them - years ago." This is referring to James Potter talking about dementors. The significance here is that the word "her", referring to Lily, is emphasized where "that awful boy" is merely bracketed with dashes. The dashes indicated a hesitation in speaking, that Petunia was searching for words to use instead of James' name. The italics on "her" indicate that the tone of her voice changed when she was referring to Lily. Combined with her deliberate avoidance of saying her sister's name we can conclude that Petunia carried more dislike for her sister than she did for James. She merely avoids his name as she does anything to do with the wizarding world, but she clearly has strong feelings about her sister.
The passages from the first book lay a foundation that is reinforced by the passage from Order of the Phoenix. She had avoided her sister for years, became upset at the mention of her name, and erupted with negative judgements when pressed by Hagrid's intrusion. Both books quoted here include reference to one event (or series of events) - the visitation of James Potter to the home of Petunia and Lily's parents. Going by the text we can see that he came to visit at least once, and that there was likely a wedding to attend as well. (We don't have any information on the specifics of wizarding weddings, but given their similar observations of other holidays it makes sense to assume they are similar to Muggle weddings.) While Petunia may have refused to attend this wedding, if their parents were alive she may have been required to go despite her wishes.
What is known for sure is that she met James Potter on at least one occasion and overheard him talking to Lily. Now in order for her to have overheard that conversation she must have not only have been nearby, but she had to have been listening - after all, she remembered what was said for roughly eighteen years. This is significant. Most people do not pay close attention to people they are repulsed by, and if they do, they tend not to memorize the topic of conversation well enough to recall it almost two decades later. Petunia is a well-documented gossip though, so it is possible this is just one of her special skills.
So we've gotten a good surface look at her feelings for her sister during Harry's Hogwarts years and made an analysis of one verifiable social interaction at least three years prior to Lily's death. If we start assembling the pieces we have, we may just gain insight into what is missing.
We can place Lily's birth at approximately 1960, which puts her graduation from Hogwarts at 1977-8. On November 1st, 1981, (the day after Lily's death) we have the first statement from the book quotes above - that Petunia had not seen her sister for several years. We also know from the books that James and Lily did not begin dating until their seventh year at Hogwarts, so the soonest he could have come home to meet her family was the Christmas holiday of that year 4-5 years before they died.
Furthermore, we know that Petunia and Lily's parents died prior to the Potters, because the Dursleys were the only familial option to raise Harry. Lily almost certainly attended their funeral. Petunia very likely did as well, given her obsession with outward appearances. Almost certainly this was the last time they saw each other. There is some speculation that their parents' death may have been linked in some way to the war with Voldemort, but we have nothing to substantiate this. The complete lack of information does make it suspicious; but, on the other hand, it seems exactly the sort of thing that Petunia would have pointed to in order to prove that the "freaks" were undesirable.
Aside from some minor speculations, none of this is anything new to those who've closely read the books. We've been given a very clear picture of Petunia's displayed feelings for her sister from the time when she was attending Hogwarts until her death. There remain a great many undiscovered pieces to the puzzle leading back into their childhood.
One big unknown is the question of birth order. Between Petunia and Lily, which is older? If Petunia is the older sister, it's likely she felt ignored by the sudden adoration and attention Lily got upon being accepted to Hogwarts. She would view her little sister as a "usurper" of her rightful position as parental favorite. If Petunia was younger than Lily, it's also likely that for the years between Lily's 11th birthday and her own, she fantasized about joining her older sister at the magical school. Imagine the heartbreak she must have felt when her birthday came and went and no letter arrived. It would be all too easy for that crushing disappointment to turn to bitterness and hatred. Lily would then embody everything she had failed to become and would never become.
Another dynamic in families with more than one girl child is appearance. Petunia is described as blonde and horse-faced while Lily is red-haired, has brilliant green eyes and by all accounts quite beautiful. Often the more beautiful daughter gets the most attention from the parents, causing the "wallflower" to become bitter and envious.
It wasn't enough that Lily was prettier. It wasn't enough that she was her parents' favorite. No, Lily had to go and excel in a field that Petunia could only dream of understanding - magic. Lily sucked up all the attention and praise from her parents. Lily had to bring home the handsome and charismatic James Potter (who far outshone Petunia's Vernon). Then, if that wasn't enough, her parents had to up and die, forever removing any chance of Petunia overtaking Lily in their eyes. Finally, Lily herself died and no matter how much Petunia might have despised her sister, that could not have failed to cause her pain. Just listen to Petunia's own words: "and then, if you please, she went and got herself blown up". These are not the words of someone who's come to terms with a death. These are the words of someone stuck in the anger phase of mourning a loss. She is angry with Lily for dying, and not just because she got stuck with Harry.
Lily was the shining example of everything Petunia was not - could never be. It is hard enough to live in someone's shadow without coming to hate them in a small way, but then to have the score permanently frozen by premature death, making any chance of victory impossible...and it gets worse still. Death has a funny way of erasing defects, making the deceased more perfect than they ever were. Petunia can not even maintain her hate without making herself more petty and bitter than she already was.
It is easy to see how Petunia is a product of her environment, and yet she is not without blame for who she has become. We all face hardships, we all have tests to overcome. It comes down to a matter of choice. Petunia chose a path of bitterness and resentment. We may understand her, we may even empathize with her, but we are not required to agree with her.