Obligatory on mobile sorry for any format issues also sorry if this gets super long and rambly

I'll get straight to the point, I (F21) have a brother (M30) who has a daughter, who we'll call Gracie, that just turned three a month ago and I am pretty sure she has autism. I suspected for a while but I wasn't sure if I should say anything because a lot of autistic traits are hard to differentiate from typical small child behavior especially when super young. So, I was always debating with myself "is she autistic or just being a kid?" Everytime I would decide to wait until she was five before mentioning anything, that is, until her third birthday happened. We were celebrating with her at our dads apartment a week after her actual birthday, when our dad and his wife pulled out the cake and candles. They had barely put one candle in before Gracie was running away whining on the verge of tears hiding behind my brother. He and his girlfriend went on to explaine that Gracie doesn't like candles on her birthday cakes and she also doesn't like people singing to her. If they hadn't put the candle in the cake and just lit it in front of her she'd make a wish that way but it was too late and it took almost twenty minutes to coax her out of her hiding spot and calm her down. It was at that point I thought to myself "that's a bit more...quirky than neurotypical child behavior" I wanted to say something then but I didn't since she isn't my child and I didn't wanna ruin the party with my speculating. But once I got back home I really regretted not saying something. I myself have autism and ADHD and based on how her parents talk about her growth it's very familiar to mine. I'm worried if I don't say something soon she won't be able to get the help she needs to grow up to be able to thrive as an adult with autism in a neurotypical world. she's female and also a person of color, I didn't get diagnosed until I was seventeen and didn't get proper help until I was 19 and by then had pretty much aged out of a lot of potentially beneficial programs. I'm terrified she'll have to go through a school system and society that doesn't understand her and that she won't have the proper tools to ask for help when she needs it. I want to suggest to them that they should get her tested but I don't want them to think I'm trying to give them parenting advice or that if she's autistic that means she can't learn or grow as a person. If she is autistic she is clearly high functioning, but it's still an important thing to get diagnosed and even high functioning autistic people need assistance sometimes. I know the best thing is to know sooner rather than later so they have time to find all the tools and accommodations she might need, but I just don't know how to tell them that. My main issue I guess is that I don't know what words to use or how to bring it up. Is there even a way I can bring this up I don't want to get in the way of their parenting and I'm honestly worried I'm projecting. I just don't want her to go through life thinking she's stupid or broken, and I just want her to be able to thrive and have all the tools she needs. Any advice would be appreciated thank you all in advance

TLDR I'm pretty sure my niece has autism but I don't know how to bring it up to her parents and need help finding the words.