If you can get Animal Planet channel, watch Bed Bug Apocolypse. It's very informative and by happenstance I just watched it last night and saw this post today.
DH is an exterminator. Exterminators are using heat a lot now (above 120F) to kill them. That program said heat is the bed bug's 'achilles heel.' A steamer can also help if you have one, but they can hide in appliances, computers, rugs, wood furniture, etc. A bed bug doesn't have to eat for a year and a half and will still survive.
They are finding bed bugs in retail stores with NEW clothing, bedding, etc. now. Also, fire halls where fireman bring them back and sleep on their bunks in the fire house.
Hope your sister doesn't have to spend too much to get rid of them, but the program said people have spent thousands to get rid of them.