You need to have more patience. You don’t give her any time to be able to absorb anything you tell her. And on top of that, she obviously has a different learning style than you do. The best thing you can do, from a teacher’s point of view, is to learn how the person you are trying to teach learns, so that you can teach them in a format that they can understand.
You can’t expect other people, or especially force other people to learn in a way that they are not comfortable with. As much as it may be difficult for you to do, you’ve got to consider your mother’s point of view and let her learn her way.
You will need to work on your patience, and not get so frustrated when she doesn’t do things perfect the first time. Everyone, including you, takes time to learn new things and new concepts, and technology is one of those concepts that is very finicky and always changing. So to jump into technology when being away from it for virtually the entirety of its progression is going to be a daunting task for anyone, no matter who you are.
It’s easy to say it’s easy after growing up with it and having it with you all your life, but it’s essentially the equivalent of being thrown into the pilot’s seat of an aircraft when you’ve never flown before. You can think about it and say ‘yeah, I can do this.’, but then when you sit down in that seat and see the hundreds of buttons, switches, screens and instruments, it can easily be intimidating enough to scare a person away from it entirely.
Now teaching something like a phone obviously isn’t as complex as piloting an aircraft, but it’s a milder form of it to a person who’s completely technologically illiterate. It’s going to take time, and mistakes will be made. What you’ve got to do in the situation is give in just as much effort as your mother is in attempting to learn it in the first place. With you giving up almost immediately, if not immediately every time she asks for help, you’re abandoning her to her own devices, so obviously yes she is going to get frustrated at you for doing so. How would you like it if you were given a new math problem in school using a system that you’ve yet to use, and the math teacher didn’t instruct you on how to solve it, yet expected you to know how to get the answer?