Well....with the details you provided, there could be 1 of 2 things happening.
1. She likes you as a friend, trusts your judgement, and knows that she can rely on you to give her sound advice--as a really good friend would.
2. She's trailing you along as a backup--which is what you are thinking now anyway.
The best solution would be to ask her flat out what she's doing. Don't stall or give her warning, or she could think up some lame excuse or lie. Just ask her to be honest with you about her feelings toward you and what is going on. If she even starts to stumble in her response, I'd bet she's playing you so that she's got a backup....however, you know her, I don't, so you should know enough to know whether she's stumbling to think up an excuse or whether she's just truly shocked that you would ask such a question.
Either way, you probably aren't going to have a relationship with this girl again...I'm sorry.

But, maybe that's for the best. Good luck!