Sometimes people who have a poor self image may treat another in the same way. Sometimes people also dislike aspects of someone else which they have themselves and don’t like. Perhaps you are similar in some ways. There are many reasons why someone might treat another badly and listing them all might fill a book…and probably has, many times!
This sounds a bit glib but love is the answer many times. People need love and respond well to it too, ironically your mum may need your love very much. In the process of showing love and not just thinking it your patience will be tested I’ve no doubt but through that your mum will receive love, and you will receive love and become more patient and forgiving in the process. Quite a lot of benefit in showing love.
You’ll probably need to show a little love and take a break quickly at first, but after a while, who knows, perhaps the breaks will get shorter!
God bless.