How do I get rid of the guilt about NOT going to help my mom who is in another state and my brother lives very nearby her home?

I've already been out to stay with her twice since 2015. Several months each time. She is now 84 and as she ages, she is becoming less able to be alone. But the only one she wants to have there is me. She "doesn't want to put any more stress on my brother who has a family (a wife who's not supportive and mentally ill, a wheelchair bound daughter and her child). Yes, he has a lot going on, but he's right nearby her.

When we first moved to another state, I asked her to come but she said she felt like she needed to be there for my brother. We moved away more than 20 years ago. Why do I feel like it's MY responsibilty to care for her?

I work from home so it was easy to go to stay with her the two times I went. But now I'm divorced and don't have anyone to take care of the dog and cat. I live in an RV that I purchased and I can't just board the animals. I bought the RV in the hopes of being able to drive it out to her if necessary but it's not as good as I thought. It has lots of little problems and I wouldn't trust driving it from Texas to California. And I am also helping my daughter by babysitting my granddaughter and I have another child who is expecting my second grandbaby in July.

I have no answers and it's eating me up. She has neighbors who are there for her but they can't do the "family" things that need to be done. I plan on trying to find out if her insurance will pay for a nurse to come in twice a week or so to make sure she's taking her meds and that she's taking care of her daily needs. 

I don't have the finances to fly out there as I did before. I feel like the guilt and knowing that my mom is starting to go downhill is causing me to go down the same path with my health. I am being pulled in two different directions. Even thinking about what I might have to do is putting a lot of extra stress on me. Help!