Other than not buying the biggest one you find (if she's not played with them before, don't wanta send her running, screaming into the night), why not let YOUR imagination go wild.....shop around and find one that YOU would like using on her. If you two are already lovers, then you know what pleases her. Go with that. Let her know that it gives you pleasure to do that, too. Oh and if she's a bit shy on the subject, go gently, talk at first. Good luck and have fun!!!