ETA, Junior sizes are for slender young adults/teen girls. They are often small in the hiney area and more straight up and down. It used to be that junior sizes were the odd numbers. Like 3, 5, 7, 9, etc... They are typically a younger style. Less low cut, for younger ladies and teens.
Women's or Misses clothes are for women that have fuller body parts, like boobs and hips from having kids or just more curvy. They were the even number sizes like 2, 4, 6, etc...
If you find that the clothing in the "junior" department don't fit her well then you will have to move over the the ladies/women's/misses sizes instead. These are typically cut fuller and have more moving room in the areas that need it.
So many designers now size everything small, medium, and large that sizing doesn't mean as much. They are more generic.
To this day when we shop for my granddaughter we go to the junior section so that the clothes will fit her better since she's thin in most parts but does have a developing chest. Misses sizes sort of hang on her.
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She is the same size as a large adult. Why aren't you shopping in the adult clothing section?
There are plenty of clothing that will fit her. She is taller than me. When I weighed that much I was in an adult 16.
You need to stop trying to fit her in children's clothing. She doesn't have a child's body anymore.
At Walmart they carry many many many clothes that are very generic, such as no darts, no low cut bodices to expose cleavage, and nothing really sexually styled. You just need to stop trying to keep her in children's clothing because she might be 12 but she has an adult body, a large/x-large size adult body.
I hope the doc can find out what's going on with her metabolism because this time of her life is when she's going to develop long time friendships and bond with a lot of people. It's extremely hard on her self esteem and self image. Even if she loses weight and is a thinner adult these internal scars can haunt her.