I've been caring for my dementia father and now my demanding mother is coming home from rehab. What do I do?

Dealing with dementia father now mother coming home from rehab and she is very demanding. I just started taking care of my dementia father since my mother is in rehab. She will be coming home in a few days. When I went to visit my mother she is so demanding and starts to tell me everything that upsets her the minute I walk in the door. I feel so overwhelmed because I had just come from dealing with issues with my father and then I see her and she demands that I do this and that. I was so angry I just wanted to walk out because of the way she talks to me and how she demands that I do this. I would do these things anyway but she is so intense. I don't want to get angry or defensive but how does one handle a person who throws everything at you the minute you walk in the door? I would like to know how to deal with her frustration. Thank you.