My dd was the same. So many unworn clothes throughout the years. She went through a stage at about 6 of only wanting to wear one dress at home and one particularly washed out school blouse and two washed out school skirts. I managed to get a size up in the skirts and washed them to death before swapping them over but the size up in blouses was slightly different. So many issues with school uniform in primary.
Her sensory issues have improved a lot now at 13. Then there was the stage maybe in yr6 she wanted all new clothes - a different style and no dresses, which she’d practically lived in until then so I bought a whole new wardrobe eg a bunch of leggings, 3 jumpers and she only ever wore one jumper, had a favourite a couple of pairs of the leggings etc. And some were not right as no one else had them etc. So an element of trying to fit in.
Don’t listen to suggestions of not buying your dd clothes and chucking out those with holes in them. It will cause her massive distress. With my dd, I would insist she wore nicer clothes if we were going somewhere special. But she liked party dresses, possibly as they were pretty, soft and silky.
If I could do my time again, I would not buy as many things. The problem was, like you, we would get things home, take the tags out and she’d find something wrong with them (itchy) or just say she’d changed her mind. She still does it now. But now it’s for fashion reasons, to fit in, as she has now the ability to know when something isn’t comfortable.
I get it. It’s really really frustrating and wasteful. Charity shops had a field day.