Hello,
I am in a similar situation where my wife will not communicate her desires and wants me to surprise her with what I come up with. It is a difficult position to be in for sure. I'll let you know how I have gone about it, though I should preface this post with the fact that both my wife and I are new to BDSM, and I am by no means an expert.
I was given some advice to try new things and gauge her reaction. My experience with this was not very good. Even though I was married and know my wife very well, we were both new to this and a few things I tried definitely missed the mark. At the end of the day I didn't really enjoy the scene and my wife had mixed feelings about it. Shortly after, I spoke with her about how uncomfortable I was and if there was any way we could talk about it more. She did eventually explain her general interests and desires and it has (so far) helped quite a bit. Even though we don't have a defined set of limits, I at least know her general attitude and that helps guide the direction of a scene to something we are both comfortable with.
I will say that communication is the best way to get the most out of BDSM, and if at all possible, get your girl to talk with you about it. If you don't communicate, you WILL cross the line eventually. Believe me, it's not fun for anyone involved.