Firefall...
Many times our loved ones refuse to help themselves (addiction; mental health; physical health) and we are left holding the ball so-to-speak.
In my opinion, laying boundaries for her as to what conditions she can stay with you is a way to keep peace in your household.
I know of one man in his early 50's that refused treatment for schizophrenia. He knew that it had a big impact on his life but he felt he was Jesus and didn't need help. The last place to live was with his sister who was at her wits end. She told him "you either get help or be homeless."
He went and got help. Did he believe he needed it? Not really but he had a choice to make as well....just like his sister.
There is no forcing treatment for any of our loved ones.....however we can figure out what we need. How do we maintain our life, in our home, without catering to the needs of someone who doesn't care? I am afraid it lies with us.