Similar to the popular Cowgirl position, she kneels on top of you, pushing off your chest and sliding up and down your thighs. But you help by supporting some of her weight and grabbing her hips or thighs while you rise to meet each thrust.
Less stress on her legs, making climaxing easier. Plus, female-dominant positions delay your climax, so everyone wins.
Alternate between shallow and deep thrusting to stimulate different parts of the vagina.