If she doesn't put in any effort to actually keep the coversation going she probably doesn't care about you and just asked out of boredom,and
if something like that happens again you can be pretty sure she's not interested in you that way.(that's what i'm thinking)
Forget her and don't focus on the past , if you find someone who really cares about you, you don't need to try to keep the conversation going it just happens naturally.