I have this in my contract:
Head Lice and Bedbugs - I MUST be notified immediately if your child or any member of your household has head lice or if you have bedbugs in your home. Your child is not to attend daycare until after your home has been completely free of lice (multiple treatments given) or bedbug free. I realize this may mean your child is going to be away for a long period of time but this rule is to protect other children and my home. I reserve the right to request a letter from a professional that your home is bedbug free.

In this case I would be asking for a professional letter saying their house was professionally cleaned and that bedbugs are no longer present. No not everyone has bedbugs! OMG, she is thinking dust mites likely.