Look after yourself. If this relationship is endangering your own mental health you may need to walk away from it or at least stand well back. You need to have a difficult conversation - particularly about her medication. It may ultimately have to go as "I can no longer support you if you choose to not take your medication and help yourself." Sometimes friendships require tough love.

I realise there is a language barrier with your friend's mother but you need to talk to her. The woman needs to be more responsible for her daughter and the daughter's health - like doing what she can to encourage her to take her medication and starting a line of communication with her daughter's care providers. You cannot carry the burden by yourself.