How can I progress rough sex?

Looking for some advice. I've been with my gf for 5 years now and the sex is great. We both enjoy rough sex with me being the dominant one, and we regularly do things like hair pulling, choking, forced oral, and if I'm feeling particularly horny I've spat on her face which has all been well received.

Me being me, I'd selfishly like to progress things by doing new things. A big turn on for me lately has been the idea of finishing on her face or in her mouth which we haven't done yet as I'm not really sure how she feels about it. I've tried talking to her about it but she is quite shy and says she can't really think about that stuff when we're not in the moment. Although she did say she wants to build up to having me finish in her mouth. I recently tried bringing up the idea of a facial whilst we were having sex by saying things like "I really want to pin you down and cum on your face" but it was hard to gauge her reaction. I'm pretty sure it turned her on but I didn't do anything as I'm worried about crossing a line and doing something she doesn't want.

I'm not sure whether she just wants me to take control and do things or if she is trying to politely decline. Does anyone have any advice?