What would you do in this case-walk away or stand up for your cause?!

Okay, I'm going to try and qualify this question as best as I can.
I had a woman living with me on and off for a couple of months. She moved in, we bought a dog together, ate the same food, shared conversation, had sex (sporadically I might add), and argued continuously. It became readily apparent to both of us that our relationship was not going anywhere, but I was still willing to try and make things work. Next thing I know, she turns around and moves out when I am at work one day-no warning was given, but the writing WAS on the wall. Anyway, she decided that the dog belonged to her (I paid for 51%) and she took a bunch of my personal belongings too. Also, she still owed me $300 from a previous loan, which she said she would pay back.
I know where she is living now and I have some potentially damaging information that I can use against her. She will not give me back any of my money, etc. Should I pursue this further, or just treat it as a hard life lesson and move on?