Sounds like you're afraid of seeming weak or not dominant enough if you admit to her that you don't know these things. Don't be. Whichever quality your submissive fell for, I'm sure it's a lot deeper than this, especially if she's your fiancée. Just ask her what she wants. If she doesn't know you need to explore it together. Most importantly, you need to figure out where you want this to go. I'm fairly certain that there's nothing more frustrating for a sub, than a Master who doesn't know what he wants from her.