I would see if you can get her to talk during sex or after. I think if she can do that, then you can make it clear to her that you would like her to initiate when she is interested and that she doesn't have to respond to your initiation if she is not. If she is tentative or wary, maybe she could give you a sign that she is interested and would like you to initiate. Maybe that lets her feel pursued and gives you the confidence you are pursuing at the right time. Trial and error. Just like everything else.
I like OneArts suggestion about talking after sex (especially if it was a positive experience for both of you. In the real world we know that's not always true for every person every time...so be aware of this).
My only addition would be to watch her response to discussing sex at this time. For a lot of people this is the perfect time to talk about sex - you're bothe vulnerable but content. But I know for me in my past this is also when I felt the most "judged". Feeling very raw but then a discussion about how to improve...can be tricky. So I'd say just monitor very closely and maybe pick another time. For me I'd rather discuss sex when out and about having fun (at a concert or a bar) and when I felt really connected to my partner - and when I felt very confident. So just be sure you do what works.
The suggestion about a subtle signal is great. Code words are fun. "Hey hun, know what I'm in the mood for? Strawberry pie! Haven't had that in forever....".
