I would suggest having a sitter with her at night. They can lock the door and have a key with them in case of fire. I would also suggest a baby monitor with a camera to help the sitter keep an eye on her.
I do this for a living. I work for an agency that supplies around the clock care for seniors so they can stay in their home. You don't necessarily have to put her in a home but you can't leave her on her own a night at this point.