I work in SEN IceBeing, I agree with whataload.
Can you try and think ahead please?
There is time for your DD to go to a suitable school which will understand her SEN needs. Regardless of her current academic progress, she is missing out on crucial life skills and is not being given a balanced view of reality.
You and your H, with the best will in the world cannot wrap her up in cotton wool. Yes, she may come across bullying, she may get a tummy bug, she may get a bit anxious. But life isn't about avoiding these issues, it's about learning the vital skills to deal with them.
Which is why I asked you to fast forward. What about when the hormones kick in? What about a teenager, who has not had the valuable years spent in school but wants to spread her wings but is too scared to? The under-graduate who deserves a university education but is convinced that the outside world is a place of fear, not adventure.
Her home environment is unhealthy, her anxiety will increase and possibly cripple because of her DFs MH issues, and bouth of your projected fears.
For all of you, and in particular his daughter's future, he has to seek help.
She needs to go to school, because what is difficult about a classroom at KS1 will be impossible at KS4. The sooner the better. A good SENCO will help with this.
The world is a scary place, but she has the right to be part of it, and to see that bad stuff sometimes happens, but she can cope and recover. Ultimately she is missing out on so much, the good stuff, the fun stuff. The learning that we are all different, but that's what life is all about, respect and tolerance.
Brutal here - but fast forward even further. To a time when you and H may not be around. Would you feel that you'd given your DD every opportunity to grow into an independent, strong adult?
I wish you all well. Your H, whether you stay or go must get proper professional help, today.