I don't think she is saying it is not legit; as she says in the video, you can determine autism in an infant at only a few months old if you know what to look for.
If anything the issue is not that society recognizes autism too much, it's that it doesn't recognize it enough. What is hurting these "transgender" autists (leaving aside the under 18s, which is its own horrible issue) is the fact that we think that if someone can hold a conversation and pass an IQ test, they're fine to send out into the world with no extra concerns. We don't have a widespread societal concept of an adult who can go to college and succeed in a tech job but cannot grasp that other adults might lie to them or take advantage of them. In our minds if you're not intellectually disabled or similar, you're good and you're on your own.
We can't even do a good job of admitting how much autism is increasing, partly due to the fact that the increase has been connected to so much bullshit in the past and the subject is now tainted (thanks, Lancet, for giving Andrew Wakefield a platform, great job you did there)
Unfortunately I don't see any way of changing this without it coming across like taking away rights, and now even a gentle "maybe we should ask question about all these autistic girls who are chopping their tits off" is ableist and transphobic and you are a bigot for even bringing it up.