Jess,
It is very difficult for people who abuse to stop being abusers. I work with battered women so I see lots of this every day. It takes a lot of work and therapy and above all else it takes a real effort on the part of the abuser to WANT to change.
There is not set time for someone to stop abusing. It can take months or years. Is he still in therapy? He cannot think that by going to two or three sessions that he will be better.
Be there for her..that is all that you can do. If you push her to get out of this relationship then you might lose her as a friend because she will feel pressured. She needs to be able to make her own decisions with her life. If she is in an abusive relationship then she probably does not get to make too many choices about her life as it is.
He can change, but it will take time and it does not always happen. If you want to help get the numbers for your local domestic violence centers for your friend. They can provide resources and counseling for you. If you like I can try to get them for you area.
You are a good person for wanting to help her.

Jessica