Red I think you have always had a real bee in your bonnet about never fulfilling your potential as a young student because of undiagnosed autism and other conditions. You like to lay blame for that at everyone you can.
As a result you've spent your life since having children obsessing over making sure your they achieve and are supported (or controlled?) to achieve, coached to go get into to the best schools you can find in your area without needing to pay (although you've suggested in the past that your siblings are terrible people for not offering to pay for your own DC to have a private education, even when you were not working and neither was their father, or he was earning very poorly if I recall.)
Perhaps because you are autistic your particular pet topic/obsession is grammar school education compared to non-grammar or 'modern school' education, as you like to call it, and you can compare and quote at random the results scores of grammar schools and other high performing schools up and down the country, even in areas where you don't live. If that's your 'thing' then by all means enjoy it.
But this girl who may or may not be your goddaughter (or perhaps your niece?) is not your toy or a chess piece to be used in your personal vendetta against a system you feel let you down. You can't live vicariously through her, trying to right the educational wrongs as you see them, that were done to you.
She isn't you. Doggedly pushing her to where you would have liked to be at her age is not going to change the way you feel about yourself. She may say she welcomes this intervention but I think she is just playing to her audience because she enjoys the attention she's getting from you.
Besides, this is about so much more than making sure she's supported in education with her autism and dyslexia. She is about to have a baby and you seem alarmingly unaware of the full impact that is going to have on the day to day life of an autistic 17 year old. You seem to think this baby is nothing more than a fly in the ointment, and as opposed to the main thing^ that everything else should be centred around from now on.
If she's asking to live with you now it's not because she 'wants' the very strict boundaries you would put in place, and you are pretty soon going to find that out the hard way.
She wants to live with you because she's an immature, pregnant, rebellious teen with some behavioural issues who objects to her mother's efforts to control her, however half hearted those efforts may seem to you. It's extremely arrogant and deluded to assume that the only reason she's pregnant and not engaging properly in education is because you haven't been allowed to take the reins and manage her life for her, and if you had it would all have been different.
Running to you now is nothing more than a way of sticking it to her mother. Can't you see that? If she says she is relishing the idea of monitored minimum homework hours and an evening curfew she's just playing you. Even if she thinks she wants that, she's being incredibly naive. She has a baby to put first for a start. Who is going to look after this baby while you are busy coaching her and helicoptering over her several hours a day? And you think you are going to draft in your mother and your husband with this project too, when this girl has two parents of her own?
You are so alarmingly lacking in understanding of what is the right thing to do here, it's unbelievable.
If you really want to help, then your focus should be on helping her not screw up this child she's bringing into the world. God knows that sounds like enough of a challenge to keep the lot of you busy.