My daughter who has OCD and ADHD started developing `disordered eating' about 18 months ago. Luckily she was already under the care of a psychologist and psychiatrist but they recommended
https://www.majaberry.com/ for some specialist help. She was good and definitely very expert in the area, so worth trying although she's not very local. I think my daughter did quite a bit of it online (she was 17 at the time). Luckily things didn't get worse and improved to the point where it really wasn't an issue anymore. The support from weekly sessions with her psychologist helped a lot too. She's fantastic and has helped a lot with the OCD. If you DM me I'll send you her details although I don't know how much availability she has.
We did all of this privately although the GP did refer her to CAMHS and they actually contacted us very quickly, so it's worth pursuing. The GP was very good and insisted on fortnightly weights being submitted which I think helped my daughter realise how seriously everyone was taking this and how potentially dangerous it could be. That worked for her, but it all depends on the child. I wish you the best of luck with this. It's not easy as the parent, but it sounds like you're taking the right approach so I'm sure that will serve your daughter well.