hmm...maybe it was more challenging for her before? Personally I've never felt this but I've heard a lot of girl say they want what they can't have. Just the challenge of trying to get you when you "belonged" to someone else.
OOORR Maybe it's akward for her now. Maybe because you're not taken she knows something could happen and she's just shy about it.
The best advice I can give you is to talk to her. Maybe not like "hey I like you do you like me" but just initiate a convo. Try talking about something she does that interests you or ask her out "as friends" somewhere so you can talk.
hope that helps a little...
Good luck with everything Lloyd