...In bed with Lydia (my fave scene of the film in fact) She says "You really shouldn't just stop like that, set a woman back three days doing a thing like that" What did she mean by that?
I, Know you appear, Vivid at my side, Claiming you feel, Love fiery enough to prove flesh real
To set someone back just means to delay something, for example "i was doing really well with my diet but that take-away meal set me back a week" meaning it's at least another week until I get on track again.
I can only assume that in this case she means because the woman didn't get her orgasm, it'll take 3 days to get back to that state of mind.