Bed bugs like head lice should not make anyone be treated badly. Head llice do not come from dirtiness and neither do bed bugs. There has been an epidemic of both in the world lately and all you can do is clean up the mess and go on.
Anyone who iis treating your sister badly because of this should be ashamed of themselves. I know of very well off people that have had to deal with both of these issues and sad to say these things are part of life. I will pray for you sister to get her home restored and be safe and secure.