oh for God's sake just let her move in and see how it goes, don't charge her anything or she'll think you're a knob.
Do not do this trust me. I have made that mistake and it's not worth thinking about. Get it all out up front and talk about it, if she is a keeper she will also be offering up solutions and be willing to contribute. I have seen both sides, my now wife always wanted to pay her way. One of my ex's though, she was the type who would never offer anything up and if you said move in for free she would have and I was blind to it but she fleeced me out of quite a bit of money in the end. I was still paying for her months after she left my life.