I would say that you need to go to one step before, i.e. does she want to have sex with you.
I am happy to be put right by the ladies on this one, but you need to learn to understand your lady's responses. We get big fat urgent boners which rather gives the game away, they don't exactly.
One hint I would give you is to note during foreplay your partner opening her legs. You won't notice this if you dive into the pussy like a bull in a china shop but as you caress and kiss her body she may well involuntarily begin to open her legs wider. Then take it from here. All that I am saying is that when someone wants something they are more likely to enjoy getting it.