I very rarely comment on other peoples posts but I think I know what your asking. I think you maybe looking at it a bit wrong, instead of hitting topics until you find out what she likes, you can just give her a direct question that gets her talking about what she likes, or is currently on her mind.
"Whatcha upto?" - my personal fav at the minute, seems to work well for me.
"So what are you doing later/tomorrow/weekend etc..?" - shows interest, is she short of time/on a schedule?
"What do you do for fun?"
Stuff like that seems to work well I'm sure there's others but I hope you get the idea.