Agreeing with everyone else, your sister needs an attorney. If she cannot afford one, then SHE needs to go to the courthouse, and discuss this with their court advisor/facilitator, and they can help her.
Your sister needs to understand that the court won't care even a smidgen if the ex-husband has a new girlfriend. They will be more focused on stabilizing the child's relationship with both parents.
Also, you mentioned alimony. She won't get what most people consider traditional alimony in Washington State. With amount of time married, spousal support can be assigned, but it is normally only for a period of time and not permanent. This is another reason your sister needs an attorney.

