It may sound very silly, but one trick I picked up that has driven all my past partners and my OH wild is vibrating your throat!
It's a little tricky to explain, but if you hold your hand over your throat and say the alphabet very slowly and drawn out like "aaaaaaaaa" "bbbbbbbb" you can feel different vibrations rumbling through your throat. The aim is to capture that vibration with as little sound as possible(takes practice!) then while doing the deed slowly work through the alphabet.
Every letter has it's own vibration frequency which emans they all feel unique, some will satisfy more then others, so just pay attention so whe you find one that really gets her going you can come back to it. Eventualy you can just cycle the letters you know she likes the most, like my cycle at the moment is "B, G, D, T, P, Z" and every now and then I throw in a random letter just to keep her on her toes, then she can't get used to the routine and stop enjoying it as much! ;)