I'm sorry you're going through this. I would not deal well with that situation. Have you spoken with your sister about your concerns? Perhaps your sister is more capable of caring for her? You can ask her if she can invite your mom to stay longer. Maybe you can have some kind of home care for her, where you can get away for some of the time.

You might consider contacting a psychologist and ask for some ideas. Or a nursing care facility; that doesn't mean you have to put her in a nursing home, but maybe they have resources for you in your situation.