In Sharia law, you need 4 witnesses to prove fornication. Bringing a charge without the evidence subjects the one who brought it to 80 lashes.

Whether or not this applies to rape is a question of debate. However in Pakistan it certainly has been interpreted to so apply. Which means that it is very hard for a woman to prove that she was raped.

See https://en.wikipedia.org/wiki/Hudud#Requirements_for_convict... for verification.