"She Fag" is an insult usually to degrade a female or sensitive male. Since a majority of people do not call most women a fag "she fag" comes in handy as an alternative insult for a woman that may be homosexual or highly disliked. Using this insult towards a male would imply that not only is that individual extremly unliked but he also acts like a woman or may have womanly features such as a clothing style or large male breasts, therefore ruining that persons masculinity or sense of self esteem. She fag can also be used as a casual insult. It may also be highly offensive to homosexuals or may be used to describe a homosexual in an negative way. And the over usage of this word by an individual may make the insult have less impact over time such as the insult meaning of the word gay, which is why one should use the word sparingly.
"Jillian has really been bitch lately and I also heard she is a lesbian, what a f*cking she fag."
Tim: "Dude I dont think I want to jump off the roof I might get hurt."
Mark: "Dont be a she fag, just do it already."
"Look at all of those she fags marching for gay rights"