How Does Annulment Process Differ From Divorce?

I am a social worker asking about a situation for one of my clients. My client married the father of her 3 youngest children about a month ago. They do not live together. Recently they had an argument, and he hit her. She would now like to exit the marriage, and would like to know if she can get the marriage annulled, hoping that would less process and money, as she is just able to house and feed her children. How does the annulment process differ from a divorce? Is this a simple process? – Janet