How do you come to terms with betrayal by a friend you helped? It still haunts me....

Have you ever had a friend you were kind to and let into your life... try to steal your friends, get you evicted and cause destruction? It happened years ago but still haunts me..

She was travelling from another country. I made friends with her and let her into my friendship circle. I even loaned her a bit of money to pay off her credit card debit. I was looking for a place to rent with two friends and she also needed a place so I let her join. Flash forward and she had somehow turned one of them against for reasons I still don't understand. No one would tell me. It was deeply deliberate. A bit SWF. I know she bitterly complained about her mother and someone else said she slept with other people's boyfriends. Anyway.... what haunts me is how cold and deliberate it was. It was like she planned it. It gave her immense satisfaction. Has anyone experienced something like this and how did you heal from it?