i've been with this girl for a little over 4 months. she says that she has never had an orgasm. she says that one guy almost gave her one and that she has came close by herself. she tells me to rub the clit hard and fast but my fingers always slip off and she never gets off. does anyone have any advice?

Don't rub the clit with your fingers. Instead, lick it up and down with your tounge quickly. Up, down, left and right. Also, move it to the side and lick the sides of it up and down. Try sucking on the clit every now and then while your're licking it.