Is my 82 yr old mother responsible for plumbing cost?

The landlord sent a plumber who charged 300.00 to remove a bar of soap from her toilet.She has alzheimers and they say she has to pay.We since have removed the soap bars from the sink area.How can someone with compromized mental abilities be negligent.She did sign the lease.Please help.She is on ss retirement.And this landlord won't even even fix the sink drains which have been broken since she moved in.Nor will they fix the stove element.