The chapter 'Snape's Worst Memory' is one that challenges many of the long held fandom beliefs. It is also one that gives us a good deal of information on the Marauders who everyone is so desperate to know about, at the same time as it shocks and astounds them.
For one, James is a complete and utter prick, and the love-haters will rejoice because Lily certainly does hate him. It's no surprise - James is simply the most teenage teenage boy encountered thus far in the series. "Messing up your hair because you think it looks cool to look like you've just got off your broomstick, showing off with that stupid snitch, walking down corridors and hexing anyone who annoys you just because you can - I'm surprised your broomstick can get off the ground with that fat head on it. You make me SICK."
Lily proves in this scene that she is not all sweetness and light, but neither is she willing to be dominated. She is a strong witch who is not to be trifiled with - when she whips out her wand, James and Sirius eye it warily. She is quick to stick up for Snape when they torture him, but when Snape calls her a mudblood, she is just as quick to drop her support, and gives back as well as she gets. However, just because she is no longer sticking up for Snape, doesn't mean she is suddenly on James's side. He's as bad as Snape is - worse.
Lily's attitude to James is particularly intriguing. She hates him - Harry wonders why on earth she married someone she hated. Lily tells James he's 'just an arrogant, bullying toerag', proving she is not afraid to tell him exactly what she thinks of him, and she is not afraid to stick up for herself either. She will not be bossed or bullied - even in defending Snape, she's not going to agree to James's asking her to date him to stop him hurting Snape. In fact, she says to James, "I wouldn't go out with you if it were a choice between you and the giant squid'.
She must go back on this later, however, for Harry to have been born. Sirius and Remus inform Harry that James shaped up, and that Lily agreed to date him in seventh year. One wonders how much of an improvement was required for Lily to change her mind so completely on this - she does not seem a person to change opinions on a whim. So as much as she hates James in fifth year, things develop so that in the end, she is willing to marry him.
Lily is a strong witch, as this scene implies, and a good one. We already know she and James were against Voldemort; what we did not know before this book was that they defied Voldemort three times, and that they were in the Order that worked so hard to fight him.
Whilst book 5 tells as many things about Lily's nature, it leaves as many questions unanswered. Why did her feelings about James change so completely? What happened the three times she and James defied Voldemort? How come we know so much about James and his friends, but nothing of Lily's? And still the damned question of what house she is in, left open. The events of book 5 is a boon to those who write about Lily, because even as we learn more about her, there is just as much we can elaborate on. With careful reading, we can learn more about Lily than we ever guessed before.