Thank you ladies for your responses! I realize I have not expressed this in actual words to my mum when she gets this way, although she is fully aware of when she is doing stuff that bugs me, but it seems like she feels truly justified in it even when I've told her it bothers me. I notice that she only gets that way when she is under a lot of emotional stress and has no way of improving things. At first I thought it was an expression of how incompetent/irresponsible she seemed to think I was and I felt really badly, but after more than one cycle of it, I realized that it was more about her than me. I just wish I knew how to help her better.
She carries incredible tension in her body when she is under stress like that too. I've offered to give her a footrub etc, which I know she really likes and needs, but she will often tell me I need to go to bed or something! I think she feels guilty just being looked after in that way. Now I'm learning to insist and she does appreciate it.
I've also noticed that she cannot relax and let me cook a meal for her, do dishes etc without getting up to help or starting into a new project when my intention is to give her a break. Her mum was extremely hard working and so is my mother, but she considers herself quite lazy. She even apologizes if she has a headache and decides to lie down for half an hour. Is there any way I can help make her feel that it is okay to do those kinds of things without guilt?