Get lots of pics of her working with the plants. If she wants to fuck you over, take her down with you, or make it look like its hers. Buy supplies with her credit card, or have her buy them for you. Make sure her hair is all over the grow area. Its a horrible thing to think, but you have to be prepared to set her up. All women go psycho. All of them. Its only a matter of time. You may not be the kind of person to frame someone to keep out of trouble, but if she is willing to do something so trust shattering like tell on you with the intention that you go to ass rape camp for 5-10 years, then will your taking the high road make your prison sentence not so bad? Keep in mind, dont be a jerk either. Treat her as she treats you. Dont destroy her trust in you either. You could also come out and make it a 50/50 thing and spread the risk and expense evenly, like adults that respect eachother.