Advice on helping daughter (6)??

So this may be a long story but please stay to offer advice.
My daughter started holding in her stools around 17m. At 18m I took her to a GI and they started her on Miralax. I was able to hide it in her chocolate milk. It was going good but she was still holding in her stools. She is an extremely picky eater- I think she may have ARFID ( Avoidant/restrictive food intake disorder ) but I’m not sure.
The only thing she will drink anymore is water. So she won’t take her Miralax anymore because she can taste it. Her diet is extremely limited. They told me that it wouldn’t take too long to get her back on track but because I can’t giver her Miralax , she is still having issues. When going to the dr. They suggested that maybe it was a mental thing as well as a physical. So we put her in therapy to help her work out her issues with the toilet. fast forward and she is 6 (7 in June) and we are still having issues. Her therapist told me that she should get tested for ADHD and Sensory processing disorder. Well we did that and she got officially diagnosed last year.
She still holds in her stools and the doctors have officially diagnosed her with encopresis.
“A condition in which a child resists having bowel movements, causing impacted stool to collect in the colon and rectum and lead to leakage.”
Simple way- she poops her pants- a lot. We haha her in pull-ups but she was regressing with peeing in her pull-up so we went back to underwear. Well I don’t want to be cleaning poop out of underwear all day so we throw them away. We have to buy her new underwear almost weekly. Her GI just keeps telling us the same thing. “We have to get her on a consistent schedule with Miralax and pooping. Because her colon is stretched out, once it’s not stretched out she will be fine to start pooping normally.” HOW CAN I DO THAT WHEN I CANT GET HER TO TAKE THE MEDICATION???
Okay. That is something that I need help with but the major issue is… she is terrified of her vagina. Like absolutely terrified. She says that it is scary looking. Since she poops in her underwear, she sometimes gets poop in her V and she will not let me help her clean it and she will not clean it herself. She just screams and screams. She says it hurt and I bet it does but what can I do for her? I’ve talked to her to see if anyone has touched her down there and she always says no. When I ask why she is scared she just says idk. I’m at a loss what to do. I don’t want her to keep getting UTIs because of the poop but she just won’t let anyone, including herself clean down there. Please help me!!!