A woman can raise her pelvis on her own. To do this she needs to lean on the bed with her legs (you can also help yourself by resting your elbows on the bed and taking your hands on the edge of the bed) and slightly bend at the waist.
Few people are satisfied with having sex all their lives (or even all night) in the missionary position alone. A man who likes to try different positions and who easily gets satisfaction in any of them is in a vital need to experience something principally new sometimes. And if his partner wants to, but is physically unable to fulfill some of his fantasies, then she needs to pay attention to her physical form. Every woman who wants to remain always desirable for a man, should do exercises on flexibility and plasticity or, at least, do morning exercises.