How old is she?
My (now adult) DD has ARFID..and has had her entire life from babyhood on.
Over the years she has been misdiagnosed, hospitalised, put in an eating disorders unit, tube fed, had a ton of mental health input (some of which did more harm than good) and finally is now probably the healthiest she has been.
But she wasn't correctly diagnosed until she was adult.. until then she was a 'picky eater' 'anorexic' etc etc .
What helped her most was being referred to a dietitian who GOT that she wasn't trying to starve herself, she simply cannot eat the vast majority of foods (she also has ADHD/ASD and huge sensory aversions). All the previous ones tried to make her eat 3 meals a day, and two snacks and it simply wasn't going to happen and simply made her more and more anxious . The good one recognised that it was couldn't not wouldn't.
Instead she found a prescribed supplement protein drink ..high calorie that is used both orally and for those who can't take any oral nutrition, that DD could manage and got her prescribed 4 a day, which meant she met her basic calorie needs, and anything else is a bonus... so the pressure was off. DD eats, tomatoes, runner beans, a little cheese, crackers and (weirdly) the occasional steak. Oh and noodles. Apples are the only fruit. That's pretty much it. Anything else is unlikely.
But now the pressure is off she can occasionally try other things. She allows herself to NOT eat out. Family meals when she's home... she can try or leave it totally and just eat her safe foods. Absolutely no pressure whatsoever. This has helped far more than any other approach. Her friends don't pressure her, her family don't pressure her... and it has really helped.
She's also on a fairly heavy duty anti anxiety medication (an antipsychotic) which usually makes people overweight.. it means she actually has a little appetite which she has never had.
Tablets... you can't force anyone unfortunately!
ARFID doesn't tend to go away in my (long...DD is 30) experience, but it can become less stressfull if you can manage expectations. DD is still underweight, and I think always will be, but she's much happier now that she and we have accepted that this is HER. It hasn't stopped her going to a good university and being in an amazing medical career and living life, but viewing it like any other long term medical condition, rather than something we had to fix was the key for her.
(I'm sorry if that's not the answer you wanted, but having lived 30 years of it I thought our experience might be helpful.. DD is well, and a lot happier than when everyone was trying to make her eat like typical people do) (She's also one of four and none of the others ever had any difficulties)