My wife and I split a few years ago, my daughter and I have been living at my mothers. I met my now pregnant girlfriend about 2 yrs ago and we are moving in together. My mother is causing big problems and won't give me any of my daughters things and is now in contact with my ex wife (bad drug user) and is makIng my life hell. She see's my daughter as her own daughter and won't let me be a parent and is using guilt manipulation and bribes to get my daughter to want to stay there. Always overiding my plans.

What is stopping you from just going to get your daughter and her things? If she calls the police show them your custody order awarding custody to you.