Bless you for taking in this kitty while her owner gets things sorted out after a fire!

First, you should discuss with the owner. Is this cat always like this? That will be important to know before you do anything. Also, was this cat in the house during the fire? AND who is the owner's vet?

Next, if the owenr says no, the cat was never acting like this, then you need to explain to her in detail what is going on and ask her to have the vet check the kitty out for what could be going on.

I am sure other PTers will have lots more ideas for you to consider.

This is not normal cat behaviour, you are right to seek assistance.
Good luck!