you need to look into white balancing those photos, and use an external flash to get rid of those shadows
Your better off paying the model a flat per hour rate for her work, dont tell her how successful her site will be, because when it isn't (like most) they won't have much respect for you.
If you dont have the money, you can do a revshare, but consider giving her at least 60% of the net profits (probably more like 75%). After all, she's the talent and your just taking advantage of that
If you give her less, you might not get future pics out of her (especially when your not making the sales).