How come you don't help her?
It's none of my business. I don't ask for help with much, but when I do I will ask a friend and if they can't then that's fine. I won't freak out and hate them for it. It's the same kind of favor, asking a friend to help you and if they can't then that's fine. That's how I see my mom asking me to do something is.
Here is a situation. It's actually happened.
Mom: "Chris can you help me move this stuff? It's just a few boxes." This means it's actually about 20 boxes.
Me: "No I can't, I'm doing homework and after that I need to continue writing." I like to write stories in my spare time.
Mom: "Why don't you want to help me?"
Me: "Nothing in those boxes is mine, and none of them are heavy, and I'm busy."
Then she gets mad at me.
I tried actually helping her for the chance she might shut up, then she listed everything she needed to be done in a commanding tone and expected me to sit there all day (it would have taken 5 hours to do everything) and do these things for her. Her idea of me "helping" is me doing everything with her talking on the phone.
She says I should do these things because I'm her son. No other reasoning behind this. Nothing she wants done has to do with me whatsoever. Just because I'm your kid doesn't make me your peon.
It's ironic. When I'm with my dad (parents are divorced for this exact reason, dad got tired of her, he's an INTP) and I see that he is working on something, he never asks for help. If I see him working hard at something then I will offer to help out of pure courtesy, because I love and respect my dad and my dad does the same back to me. I don't feel any respect from my mom at all. He will never ask for much regardless when I offer, it's always "Can you hand me that tool?" or something along those lines.
My advice to you would be to pace yourself. You can't cram in everything all at once that you want to do. Make a list and do the things you want to do in order. If you try to do everything way too fast then you will just get stressed out and nothing will get done due to that.