I have said maybe to guys that I wasn't sure I wanted to go out with, but wasn't sure I didn't want to go out with. Maybe sometimes actually does mean maybe :P The way to get it into a yes is to be specific. There was one guy who asked me out, and I said maybe. He said cool, things are a little busy right now, but I'll get back to ya in a couple of weeks if you're still interested. At this point I was like "ok...hm maybe I should have just said no, because I really don't know him all that well, and I don't know if I want to date right now, and I'm busy and blah blah blah". But I said it sounded good and to take his time.
A few weeks later he texted me to say hi, ask me what I'd been doing recently. I told him and we chit chatted for a little bit, but not too much. At that point, he asked me if I was free that Friday between 6 and 9. I said maybe and asked why. He said he wanted to take me to a movie. I asked a few more questions about what the movie was, where we'd be going, etc., and again said maybe. I was prepared to hang up, but then he said that he'd really like to get his plans worked out, and if I couldn't do it this weekend it was fine, but to tell him now. I ended up saying yes, even though I wasn't sure, and we had fun.
Moral of the story: be assertive and have a plan. Force her to make a few definite decisions. Maybe does not necessarily mean no. It will only mean no if you handle it wrong. Good luck mon ami!