Physical & Emotional Abuse Support Group
Abuse is a general term for the treatment of someone that causes some kind of harm (to the abused person, to the abusers themselves, or to someone else) that is unlawful or wrongful. No one deserves abuse, period. Abuse can be emotional, physical, or sexual.

"That must have hurt."
"Yes, it hurts."
"Yes, it was hard."
"No, you don't want this."
"No, it's not your fault."
"Yes, life is hard."
None of those statements put blame onto yourself, or anyone else, but they all validate what she's feeling at the moment. Try to give your mother 15-30 minutes of support daily.
If she will allow you to, give her hand a gentle squeeze or hug her.
Try to understand that it will probably take about a year for your mother to get completely used to the divorce. Meanwhile, try to spent time with friends, studying, at the library, or other things away from home.