Have you ever tried gently pressing on the back of her head to slowly force her face down toward your crotch?

Yeah ... that doesn't work.

It seem like a subtle form of communication, but somehow it's always taken the wrong way.

It might be that she's not really sure what to do, or is just uncomfortable with it. Or it could be something totally different. My wife has TMJ, so she can't take my huge bulging man meat into her mouth woithout having her jaw lock up for a week.