Not having one's mother on one's side is brutal, no other way to put it.
But I think she needs to be told in a rather blunt fashion, there WILL come a day when she will be if lucky to get old enough, to need you, and you might be well long gone at that moment.
She gave birth to you, but it does not imply ownership. She has a lot of responsibilities, and you can tell her this parent doesn't think much of her parenting skills if she doesn't knock it off. She can be sad about losing a daughter, but she should be glad she gained a son. And she should be just happy she still has the person.
You might want to ask her how she would feel if you went around telling everyone she was dead, or you are adopted and she's crazy, or she's a step mom and merely hates you.
She seems to honestly believe her crap is going to be the problem though.