What can I do if Paternal grandmother is trying to get custody?

My 18 year old niece had a baby. He is one week old and she was served with papers from the baby's dad's mother for full custody. This is for the grandmother, not filed by the father of the baby. My niece lives with her parents and her sister and there is lots of love around for this innocent baby boy. What are the chances for the paternal grandmother to get custody. The grandmother has two assault charges from the 90s and the baby's dad has to possession with intent from 4 years ago. There is no criminal record in my sister's family. This grandmother didn't even get involved until the eighth month of pregnancy and has been harassing my niece prior to and even during the birth. So much that my niece had to put restrictions on her room prior to her labor. Any advice would be appreciated.