It's awful that her parent's are calling her these names. I can't imagine the pain she must feel having to hear this. Encourage her to be honest with them. Whoever did this to her needs to be put away and face the consequences of the law for what he did.
Sometimes society makes it hard for a girl to come out about date rape because they say it basically comes down to a "he said, she said" thing. But she needs to at least do herself justice by being given the chance to be heard out. Telling the police can be part of a healing process of letting go of shame, to know that she did nothing wrong.
There are people out there to help your friend. If she does not feel like talking to someone face to face just yet, or doesn't even know who to turn to first, encourage her to call a hotline. They can help her to sort some things out, determine what steps she wants to take. The hotlines are there to listen. She could try one of them or all of them.
Most of all let her know that people will help her and believe her. To keep telling people until something gets done about it.