Claire I am sorry that your flatmate says things which make you feel anxious. I agree with what Gargoyle said.

Sow seeds for the kind of garden you want to live in. Note and remark upon the kindness and talents of carers and residents. Sit and talk, sing or play a game with distressed resident(s) when staff is overstretched. Both residents and carers will appreciate and reciprocate when and if possible.

I hope your flatmate's weeds will soon become flowers and fruit in that environment.