I was like this as a teen
I was also incredibly naive and vulnerable
I now have my autism diagnosis in my 30s xx
I agree with your concern in your op. Bad things can happen to girls with autism, who seem able to cope with the world. People take advantage and youre a target for bullying. And it doesnt age well and becomes noticeable after a while.
Could you have a frank conversation with her? Is she going to uni?
Maybe you could frame it as a series of life lessons. Set up your own mini curriculum of things you need to teach her such as
Male attention
What to expect in a social situation at work
What to expect at a party
What to say and not to say in various situations
Maybe you could draw a diagram of friendship tiers and how to behave among each tier, ie:
Close friends - completely yourself
Aquaintances - more reserved
non friends, etc etc
Autistic people in my own experience need to be taught about each specific social scenario to be adequately prepared for them
Above all, its important that she knows that she is loved for who she is by her mum.
That she has her diagnosis and understands that she needs to spend more time than others working out how to socialise
Best of luck ❤️