Serious: WIBTA if I told my Baby Cousin she very likely has Autism?

It's a hot topic for family atm: My cousin (9F) is known as "eccentric". In Autism-terms, Imagine nearly any Autism-Stereotype, especially for young kids: Everything is too loud, fabrics are "wrong", touch-avoidant, classmates are "childish"/doesn't socialize by her own very much, very clever but needs time processing, very clear routines/things have to be done a certain way, food cannot touch, many foods can't be eaten cause "feels wrong", a hyper-interest in the show Ladybug, cars & the indepth history of Berlin. Oh yeah: And she doesn't talk. She CAN talk -she just....doesn't. Just stares at, shrugging, gesturing or otherwise hoping you'll "get it".

I (22F) have AuDHD. Diagnosed & interacting with the topic for 7 years. But even then, not one is really listening. My Aunt is "fine" with the idea...however, she doesn't pursue a diagnosis, as long as the doctors won't give her a referral + she doesn't see a need yet . Ironically, still the best reaction of all: My Uncle (her dad) SCREAMED me into the ground when I first mentioned it. "I'D KNEW IF SOMETHING IS WRONG WITH MY DAUGHTER! YOU ARE NOT AUTISTIC EITHER! YOU'RE BOTH NOT LIKE THE NEPHEW OF MY COLLEAGUE!" (yes, he brought that cliché) He later calmed down a bit later. Luckily. Typical "misinformed choleric Boomer with untreated childhood trauma" -but till now he insists she's NT.

Rest of the family is pretty simple. Especially my parents. My mother insists I'm projecting and "kids can be eccentric without being autistic". My step-dead (also high-likely autistic) agrees, but argues "and now? What would she do with that info? Besides: Aren't we all a bit autistic?" Referring to the overreaching "she's doing fine atm" sentiment. And tbf. she luckily does. Till now, she hasn't been bullied. And her mother won the battle against my uncle, to send her to a more accomondating school, after already going to an elementary where she was a teacher. So...why do I even get this idea?

Well. As said, she's 9yo. Soon a tween, soon going to Secondary School (~ Middle School for Americans). Aka: Soon becoming a teen & meeting the Lord of the Flies world of teens that 100% will not miss her "eccentrism". Worse: Yesterday, we were talking. It was a small point, but it turns out she didn't even know what a period was. My aunt is hopefully going to teach her soon (you're supposed to teach the basics at 7-9yo, so they don't get jumpscared), but it made me worry how little that kid is told in general.

Don't get me wrong: I don't want to impulsively yeet her into the topic. Especially since I'm "just her cousin". At 9yo, it might even be a bit...confusing? But I also don't want to idle by? Let her feel like she's "broken" when people indeed bully her?^{(Idc about my uncle's reaction. He has no power. Shall he scream until he's blue})

WITBA if I did at one point? At what age/time would you recommend? Now? Later?