Undo her bra while her shirt is still on and she'll likely take them both off. You can also just slip your hands under her bra if you're having trouble getting it off (I tend to fumble around with those fucking clasps; I need to see what my hands are doing in order to perform tasks like that
), although you could always get yourself one to practice on (think I'm joking? NO! I'm fucking considering it, so maybe you should too!). Undo her pants, then you'll be able to fit your hands in. Just don't try to do it all at once, undo the button, then back it off and if she goes to do it up, take hold of her hands and intertwin your fingers and hold her arms above her head while you pin her against the bed/wall and continue kissing her mouth/neck/ears.
Take her hand and put it in your pants, cause denim ain't exactly pleasant feeling in my opinion, which may be one reason why she isn't so into you rubbing her down below. This will make her escalate on your, which then makes it ok for you to escalate on her, cause "fair is fair" and since she already made the first move, it isn't you taking advantage so much. I find a bit of a wince as she rubs your dick works well, cause then she'll be happy to do it in a way that doesn't hurt you (no I don't fake this, as I said, denim fucking hurts).
Use your mouth. Kiss her. Everywhere. Kisses are much more tender than a groping hand and much more often welcomed. Although, if it isn't good smelling or tasting down there, I would switch to fingers.
Remember to be gentle with your hands, which may be another reason she may not be enjoying your rubbing; girls are no as fond of a firm hand as guys are. If you don't believe me, then notice how she touches you, she is probably much more gentle with you, than you are with yourself, so try to adjust your touches of her accordingly.