How do you tell someone they have body odor?

I have a HUGE problem. My sister smells really bad, she is very over weight, does not wash her clothes and rarely showers. She was bullied terribly from elementary school to high school as she is hearing impaired so when people comment about it she just says they need to mind their own business or that they are b*tches. I am concerned because I want her to be bhappy and healthy and I would like to spend time with her, but I can't because it makes me nauseus to be around her longer than a couple minutes. The whole family is concerned but we don't know how to approach her without seeming like a bully and her actually take the comments seriously. PLEASE HELP!