Don't push her but when she's really horny ask her some questions. Like does she ever fantasize about having two cocks to please her or does she ever wonder how it would feel to have another woman eat her. Stuff like that.
When my wife and I were first married she wouldn't tell me her fantasies either. But now she tells me about her fantasies and previous lovers. It get both of us hot as hell and we get off big time

Good luck.