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