Send the letter?

I have decided to write an email letter to my Mom sharing how hurtful her remarks and treatment of my son have been to him and to me. I don't know if this is a good idea, but I have never been one for small talk, nor for putting on a front with people. Her recent remarks that my son "has not done anything to be a grandchild" have crossed the line. We lived in the same state, 20 minutes away when our son was little. She never came to see us, we always had to go see her. She was in her 60's then. Then when they were in their 70's, they moved 10 hours away back to the Northern U.S. He has sent letters, drew artwork and mailed it, sent photos, drove up hours with wife and children to see her when she came to our state. He isn't good with making phone calls, even to me- because he has a wife and 3 kids, 2 dogs, and THREE jobs to support his family. SHE has never called him, won't text him, and only once written an email to him which was condemning and deeply hurtful. It took him 5 years to get over it yet he sent her and Dad photos during those years. My son is about to tun 35.
I no longer want to call her because as I said, I don't do small talk or put on a front- hiding how I really feel. I don't want to live the rest of my life carrying this hurt from my Mom gone unexpressed, but it could backfire on me too.
(sigh).
I do
I realize I am asking for opinions, and that I may not like every response, but I wonder if anyone else has been through this type of thing with an aging parent?
Mom is 91, has congestive heart failure, and my sisters and I agree that some level of dementia has set in and she is nearly deaf. A written communication is the only way I can think of to share this with her. What do you all think?