I would suggest your sister call the hospital/facility where she is getting care and ask to speak with a social worker. The social worker should be able to help figure out a plan and hopefully will advocate for her directly with the insurance company. If they do not have a social work department, she can try calling the American Cancer Society and see if they can help her sort this out. As a last resort, she can try going to the local newspaper/TV station and see if they will put her story out there and embarrass/guilt the insurance company into action.

I'm so very sorry you are all having to go through this.