Business

Was making a business plan with a potential partner. She was a roommate and we had similar ideas and offered ideas to each other since we wanted to do the same business. 
We planned on doing it together.
She stole the name and trademarked it.
She is going by another name though. 
What can I do ? 
Edit: Sadly I have nothing in writing because we were spitballing in the kitchen.  I have messages of her saying she registered a name but it wasn't ours. Then saying she did