Frustrated daughter. Why do I feel guilty?

Please take some time and back away from this situation. Your mom is angry at where her life is now and she wants everyone else to feel as bad as she does. As you see...it is working.

You can't make her happy until she wants it for herself. Take care of yourself now.

You feel guilty because you are a good person and want to help her. If you were nasty and selfish, you would not feel guilty.
Your mum is acting out probably because she is housebound and frustrated. That doesn't mean she can take it out on you, especially in front of your son.. he doesn't need to see his mum treated that way.
I would tell her that you are happy to be there for her if she is able to treat you with respect and kindness and that you are only interested in a positive relationship with her but if she does not want to do that then it is her choice that you stay away. The decision is up to her, don't feel guilty if she makes the wrong choice.

It’s never wrong to guard your own emotional and physical health. I’m glad you have. Maybe the guilt is really sadness that it can’t be better or different.

I feel your pain all too well. You are absolutely correct; she is absolutely in the wrong. Stick to your decision. If you don’t, she will continue to treat you poorly. By backing away, she will have the opportunity to see all that you do for her and start appreciating you.

Because our moms know exactly how to push the control buttons, they did install them after all.

You are right to back off, she needs to see exactly what you do and then apologize for being so ungrateful and nasty.

Keep your boundaries strong, it will serve you well in the journey ahead.