The Boundaryless Family and the Virtues of Estrangement

I called my ancient mother, who is determined to get on a train all alone, without her walker and without her cane to sit by the bedside of her sister, whom she has never liked, and who is now dying. I did try to suggest Mom might like a traveling companion, but of course this is none of my business. When are such things my business? She can barely remember the name of the relative with whom she's staying, and her assisted living residence nurse cringes every time she wanders off without the cane or the walker. . .  which she's always doing. Meanwhile, Mom insisted she was fine, that "it's just a train ride," and that by the way, how had I known my aunt was dying?
Her daughter, Cousin X had told me, said I.
"That's nice. By the way, did Cousin X mention her son is having surgery to become a woman?"
"No, she hadn't," I said. "So now we have a transgender relative," I added, since Mom seemed to expect me to say something. I took a cheerful tone, as is always amenable to her, perhaps especially when her sister is dying. 
She must have felt utterly disappointed that she had not gotten to deliver the shocking news that her very own sister and my aunt was lying in a bed in a hospital and was never, ever, going to come out. She had to top that news:
"Oh, and he's now going by the name of Y," she said, offering his new, feminine name, which does not begin with Y, and yes, curiosity drove me to look the kid up on Facebook.
Why is Mom rushing to the bedside of an unconscious sister after a lifetime of undercutting her? I can imagine a cartoon balloon spelling out Mom's thoughts as she holds the dying woman's hand: "I won, because I'm older, but lived longer."
It would never occur to Mom that Cousin X might like to be the one to tell me about her son. Or not tell me about her son. The son, or daughter-to-be, might have his own wishes about what, when, and where to tell relatives about his transition. 
Cousin X had, however, a few months ago, sent me her sister's very thorough genetic tests revealing a particular illness. Had Cousin X asked her sister if it were okay to send me test results? I didn't ask. But I don't tell these folks anything at all about myself. Back in the days when Mom invited my ex-boyfriend out to let him know she would have married him, I thought I still had to let her know some things about my life, because She Is The Mother. 
But I don't. I send her just enough information--a cute photo here, a funny story there--to keep her from asking too many questions. 
Meanwhile, the relatives tell me to give Mom "plenty of TLC." Oh, I do. I call her and I ask how things are going and how she's feeling.
"Fine!" she says, adding, with unmistakable relish, that her sister "is breathing through her mouth now!"
P.S. She skipped the funeral. Her sister died, the excitement was over, my mother felt she'd gotten what she came for, and she went home on the train. All by herself.