I think I would introduce her to a therapist first, and maybe BDSM later.

A woman living a two year long relationship with a man that treats her like a whore that isn't in a BDSM relationship sounds like a woman with low self-esteem and possible abuse issues to me.

I don't think the questions I would ask her would be about BDSM, but instead about how he treats her and why she lets him do it.

At least these are my first thoughts based on the information you have given me.