Again, thank you for all the wonderful advice, I'm much calmer now and able to think more clearly. Here is the text I sent her. Sadly, she has not replied.
Ra-—, after much consideration for you and what is best for my family I urge you to seek help at a shelter. they have many resources, including security and counseling for victims of domestic violence. With all my heart I hope you know that I care about you and your welfare but I must protect my granddaughter from any and all risk of danger. These guys can be unpredictable, there's no telling how he will react when he gets out and finds you've left him. I will be here for you and we can talk about living arrangements once things have settled down and the shelter feels it is safe for you to leave.