How do I tell my sister her visits cause more stress for me while caring for our mother?

A fellow caregiver asked...

May I please ask -- I am caring for my mother who has been in bed for about 5 years now. My out-of-state sister is very challenging and may come to visit. If I feel so overwhelmed caring for my mom, is it ok to say that my sister just cannot come right now? I hope not to hurt her feelings, but she is sarcastic, finds everything to be a joke, and I have little energy to find anything to be funny. Also, she is very controlling and that is the reason for her visit -- to try to get my mom into a nursing home and control what is going on. She wants me to go live in a home with 7 elderly people, sell my home (possibly with the idea that the money goes to her). I am afraid of her, and it only takes a few minutes for me to be in tears in her company. Any nice way to say, just not now -- I am too overwhelmed with the care of my mom. Thank you so much. Blessings to you.