Text contract

I had to ask my roommate to move out after we felt it was no longer a suitable living arrangement for either of us. I originally asked for part of November rent and 2 months rent for leaving early. As breaking my lease on the apartment was the same. We agree to set amount. I said as a curtsey she didn't have to start payments till the start of the new year so she could enjoy xmas. When it came time to pay she stated that this was unfair. So we can to a new agreement. I have in text message that she agreed to pay $800 dollars for her portion of the rent over a 4 month period. She has paid the first 200 and now refuses to answer a text or call. Do I have any legal right to take her to court for the additional $600?