I could not see any major cracks in the foundation in a walkaround, but clearly the water in the crawlspace (damp, not standing water that I could see) came from somewhere! 

For that matter if someone she knows gets it the reason will be that when you brought that diseased ridden person in they touched something, it got on her clothes then she saw her mom. 

We couldn't drink the water but we could finally wash clothes at home and not a laundromat. 

After several days of heavy rains, a tenant (who we have already had multiple problems with) sent a message stating that her roof leaked and ruined her bed and clothing.

Upstairs, I cut an access door to the attic above the kitchen, which we use as a clothes closet. 

Who buys your clothes and food?

You will soon learn that you don't know what's behind the couch, paintings, wall hangings, curtains, etc until all the tenant's personal property is out.Other pros on BP can tell you how many times a pile of clothes on the floor was covering a 3rd degree iron burn in the carpeting in a bedroom.

This is very strange and could be an issue with moisture coming up from the ground into the house; "rising damp". 

You should be able to get with your insurance provider and reduce the amount of coverage on personal contents to only cover your appliances, etc. since you don't need coverage on the tenants personal property (furniture, clothing, etc.).

A de-humidifier alone will not solve the problem, I'm talking puddles down there, not just "dampness."