Mom with dementia. How will I get through the next week with her and the guilt of not wanting to be here?

I live two states away and come home for Christmas. My husband goes to his mom's house and she is healthy and he has lots of family. Both my brothers died and my mom is miserable to be around. Her house is dirty and cluttered and I literally bring a sleeping bag in to sleep on. Her dog had so many matts, it took me hours to get them out. When I try to offer my help or outside help she gets angry. There is no food in the house and I am so sad and depressed. How will I get through the next week with her and the guilt of not wanting to be here? It’s my vacation! I work hard and then to spend it like this? I know that sounds selfish, but she is not nice to be around.