Why don't you just use something soft like a bath robe tie, or a couple of neck ties or even some furry handcuffs and give her some incredible oral sex while she is bound, then release her for any "main" event envolving coupling. Who knows she may just start asking you about more kinky things herself then.

Blindfold her and feed her works good too for a more romantic induction with out any direct sex.

of course yu could just sit her down and talk about it too, but romance is a more fun way to test the waters isnt it?