I don't know anything about ADHD but I have teen girls and this sounds like anxiety manifesting itself big time.
This programme (although it's a comedy) explains the science behind the development of the teenage brain and is really worth a listen:
Google - BBC sounds - The Infinite Monkey Cage - The Teenage Brain
(Sorry can't seem to link for some reason.)
Also Google "ARFID" Avoidant, Restrictive, Food Intake Disorder.
It is very common among teenage girls, particularly those with ADHD and it sounds to me like your DD may have this.
In your shoes op, I would be doing everything I could to take your DD "out of herself" and "out of her own head" doing lots of different activities if possible. Does she like nature, or animals, cycling or art, jigsaws, or shopping... basically the aim is to distract her big time to help her through this hump.
Maybe construct a very simple timetable together, something very undemanding, so she does the same thing every day and finds it reassuring eg, get up and dressed by 9.30am, eat breakfast (however small), go and stroke animals at open farm, or or walk a dog, or collect autumn leaves (basically anything that is undemandingly physical but outside at same time) home for lunch, jigsaws and board games, nap time etc etc. Or just let her help you do chores or go for a hike ride with her.
I personally would restrict the time she spends alone on a screen.
Also she needs some help from a licensed psychologist who specialises in adolescent mental health. I know it's not easy when they are not cooperative, or the fear is making them intransigent and you are so worried about her, but don't go too far down the rabbit hole of fear with her, let her know you are there and treat her sympathetically but equally keep modelling "quiet cheerfulness", "normality" and "reassurance" and keep the lines of communication open, listening to her fears but not dwelling on them. Let her know she is loved and that loads of other teens go through this sort of thing so this is normal for adolescence. She may think she is the only person in the world suffering like this and that's a scary thought so let her know she is not alone and loads of teens have similar issues, especially after going through a pandemic, which basically comes down to the plasticity of the adolescent brain. She needs you to be very steadfast right now so sending you lots of strength and patience. I hope the GP is helpful 