How to cheer up my best friend?

She recently split with her fiance of 4 years, he has been going out loads with his friends at weekend's and not doing much with her. They went on holiday but he didn't tell her his family were also in the same resort so they got no proper alone time. He was extremely cold towards her. They were also planning on starting a family.

He was texting her begging her to take him back last week but then pictures were put on fb of him all over this other lass we know (she has a reputation as easy). Some of the pictures were even taken down coz they were quite rude. His hand was down her top on one of them.

My best mate had a feeling about this girl a few months ago and now she thinks that he was cheating on her before the split.

She's absolutely devestated, she was in the " I'm single and ready to enjoy life again" stage a few days ago and now she has gotten all depressed and is blaming herself, even though it's clearly his fault.

I don't know what to do to cheer her up, she won't come for a girly night out or a pamper Day, she says she doesn't care anymore. I've never seen her like this. How can I help her snap out of it?-