I have a friend that is married to an US citizen, but does not yet have her green card. She is involved in an abusive marriage but does not want to get a divorce or even report the abuse in fear of losing her ability to stay in the country. What are her options? If she leaves the marriage prior to the final approval, does the process end?

Does she want to keep getting abused?
She should worry about her health.

http://www.uscis.gov/portal/site/uscis

From the INS site:

How Do I Apply for Immigration Benefits as a Battered Spouse or Child?

Victims of domestic violence should know that help is available to them through the National Domestic Violence Hotline on 1-800-799-7233 or 1-800-787-3224 [TDD] for information about shelters, mental health care, legal advice and other types of assistance, including information about self-petitioning for immigration status.