First off let me applaud you loudly for taking this step.  Many in similar situations are too ashamed to admit it to others.  Your mother is one example.  

Unfortunately, this is a large complex problem, which we can help only minimally online.

Google  abused women help
Which resources look useful to you?

In the United States, many cities have shelters for abused women.  Contact the closest one.  She needs to know that she has options- there is another way to live.  

I am not an expert, but apparently getting the police involved lessens the risk to her in sometimes.  http://www.lib.jjay.cuny.edu/research/spouse.html

Other resources
Join a Codependent's Anonymous group or similar.
Many churches