Your poor sis! She has to know that this is pretty common nowadays. Look around online. Talk to others who have been through it. It's very difficult and most unaffected people aren't sympathetic. They're just freaked out by bugs. She does not have cooties! I can't emphasize enough how common this is becoming.
I travel. I am well aware how often my fellow travelers take bedbugs home with them from hotels or even luggage contact. All my stuff is in bags in my luggage. I bag up my luggage when I get home. I do my best to prevent an infestation and my best is probably not good enough.
I don't buy anything used anymore. That's sad but that's the way it has to be. I'm also aware that a new fabric purchase or just about anything online might cause problems. Ugh!
I have wood floors and old wood, detailed furniture. I would never be able to get rid of the horrid things without gutting this place and throwing away family heirlooms.
Keep your chin up, sis! Talk to people who are supportive. You don't deserve this horrible, stressful situation. Persevere.