Oh, your poor sister. I really feel for her! What an absolute shame that she has to go through this.
I had a bunny that my husband accidentally let out right before he deployed. The bunny brought home fleas. I was seven months pregnant and while trying to organically kill the fleas (since I couldn't use chemicals), I went into pre-term labor. I brought home a premie and was mortified that she started getting bit by fleas. I had no family around and nowhere to go with my son and daughter, so I had to endure the bites. I had had an emergency C-section and was released the next day on a hospital error, so I couldn't even drive a car, let alone push a steam cleaner. Fortunately, my aunt drove 16 hours to come help me. She had to steam clean all my carpets and furniture, and wash all the clothes and linens in the entire house. (The bunny was given away too!) It took her a week of hard work. I was so embarrassed by my flea problem, even though it was through no fault of my own.
My heart goes out to anyone who has had to endure a pest infestation of their home.