I forbid mattresses and recommend they store all clothing in water-proof containers.

LolI didn’t know you can rent mattresses!

I once stayed in a beautiful cabin with an amazing hand made log king size bed, the mattress height side rails were logs with the bark still attached.

So, I move her into an empty unit, as the ceiling plaster had fallen down all over her bed, which was just a mattress on the floor. 

And for all you know, she has a bundle of cash in the bank or under her mattress that she's been saving for the inevitable day.She is not your mother.  

We had to remove baseboards, pull up carpet, replace boxsprings, disassemble furniture and put it out in the shed (at -25C for a week).By the time we were done three treatments of the entire lower unit in the building and inspections of the upper unit to ensure they had not spread that far and had replaced mattresses and boxsprings -  we had spoiled the better part of $5K.Since it was a rooming house, we had to act quickly and assume the costs - the tenant skipped anyway (and has no money).  

Why is he charging for mattresses? 

The reason I say this is because you said she left all of her personal property - not just some old mattresses and furniture.Do you have an emergency contact from the tenant application that you could reach out to? 

I think that is too high for 100 items (some of it is large like a mattress, dresser, chairs)...I am looking for someone local at this point to trash out and I can provide a dumpster for around $500.Thanks for sharing your experience.

They sleep on mattresses on the floor.