Many Hogwarts students (and teachers, for that matter, because they are in no way immune to watching their students' romantic drama like the world's best soap opera) have wondered what exactly made Lily Evans change her mind about James Potter. She's not generally known for doing that. As a rule, as soon as you cross her badly enough, no matter how much she liked you before, she will instantly and completely write you off. Severus Snape, of course, very publically learned this to his dismay in their fifth year: the day before they were best friends, and the day after, she had decided, nope, sorry, you may now one hundred percent go fuck yourself. 

The secret is that there are exactly three categories of people in Lily's estimation, no less and no more: 

1) Her immediate circle of love and concern, who she will unhesitatingly kill and die for. 

2) People who are irrelevant. 

3) As previously noted, people who may one hundred percent go fuck themselves forever. 

James was never actually in group 3; he just mildly annoyed her. 

In any event, more to the point, Lily is currently floating in voidspacetime, having just set off the philomancy equivalent of a nuclear bomb, and as far as she knows, everyone in group 1 is either dead, dying, or not nearly as trustworthy as she'd like. (She would still do murder for Remus Lupin. She would empirically not, at this time, trust him to know where her house is.)