well, if you want your frd to really resist, just tell her to
act like a "dead fish" when she's being forced, dun show any
emotion of "disliking" or "hating" sex, but instead, show him the
look of being very sianz of sex, or like acting that his bf
"skills" are terrible, that will put off her bf advance..
(e.g when he's in-outing, then, ask your frd to act like looking
elsewhere, or bo chap him, he'll feel very dis-interested soon)