I am trying to walk in your shoes. Don't know anything about your past with your mother over many years. Maybe there was something that you did a long time ago for which your mother has never forgiven you? Please forgive me for saying that. But, your situation does make me wonder. Some parents have great difficulty in forgiving their children, especially if they have been perfectionists in the way that they raised them.
So many times with family, we end up playing the same old tapes in our heads, especially if there have been some serious issues and hurts. I grew up in a nearly totally dysfunctional family. Tried many times with another sibling to try to make things right and to get along. Finally, just had to admit that I had done all that I could and just move on with my life. "Senders okay. Receiver needs some work." You may just need a fresh look at an old problem armed with some new strategies and ideas.
In yet another attempt to speak with your mother, I would suggest trying the following.
Tell her how you feel without putting any blame on her. I know that sounds really tough. But, it can be done.
I would say to her, that you have a problem and would she help you to solve it? When you state it as being your problem without blaming her in the question, then that will put her defenses down and she will be more likely to help. It puts the "ball in her court." And, makes her feel important because she will think that she is valuable and in charge because she is helping you to solve your problem. This is called winning without intimidation. It is taught in an excellent book that I recommend for anyone to read. Winning Without Intimidation
The fact that you have stated that she says that you are overexagerating, makes me think that you might have come on to her by blaming her.
Tell her, "I love you, mom!" I once knew a secretary at a school who, even though she did love her mom, her mom died suddenly, and the secretary deeply regretted the fact that she had never told her mom that she had loved her. I never told my dad that I loved him until the last year of his life when I knew that he was dying of cancer.
Tell her how proud you are to have her for a mother and why. Your presence, thoughts and words mean much more that any "thing" that you can give to a person, if the only way that you are showing you care is by giving someone a thing. Tell her that you would like to be closer to her as a daughter and that you haven't felt close to her in a long time. Tell her that you feel that you need a healing between the two of you. Ask her what you could do to solve the problem? Ask her if the two of you could work on ways of making the two of you closer? Tell her about the things that you do enjoy about her. Her caring about your brother could be one of them. "I really appreciate the fact that you are working so hard to help Chuckie. How could I help with that?"
Avoid the "yea, buts" in the dialogue. Those types of statements are defenses that lead to further potential conflict/arguments..
If an in-person meeting with your mother does not work because she keeps playing the old tapes of her usual responses, then I would try and put something in writing to your mother about what you read above. Also, I would do it in handwriting and not typing.
Nothing brilliant here. Just some fresh thoughts and ideas. I don't know all about your situation. But, I do know about conflict in a family and how to try and make peace within them so that all work together as a family.
By the way, I really enjoy reading your responses to the posts in this forum!