Personally, unless she's extremely overweight, I'd totally ignore it. My DD was always in sizes significantly larger than her peers in absolutely everything, but comparing them now, quite a few years down the line, she's well over a foot/two taller than many of her peers. Those DM's that made really snide comments, asking how big she was, got a "can't remember, off hand" thrown back at them which was actually true. I couldn't remember her size. I even used to cut the size's off, etc, carefully, because some of those DM's 'helped out' at PE time. I knew without doubt the DM's looked, but I knew that without doubt; enough to guarantee it. Additionally, I knew that labels always irritated my children's eczema prone skin, including their pj's.
We actually lived in a small village, and walls definitely tended to have ears, oddly enough! I used to think 'ffs why do these 'adults' care/give a toss?!' Haven't they got bigger, more important things, to worry about?! 🤔
They would talk in the local post office, which sold everything, you could possibly imagine, and if it went silent when you walked in, you just sensed what the conversation was about, as so many faces were blushing🙄 and conversation became suddenly stilted. Ironic and highly funny, I always thought. One day, you'll see...
Now said DM's can see for themselves why DD was always bigger than their little darling's! Plus, I'm rather tall and so is my husband! That should have been a somewhat huge clue... I had the same snide comments from paediatrician, health visitors, doctor's and the other mother's too, regarding my DS. None of them could still see the writing was literally on the wall. DD was off the centile line for her height. I had a distinct feeling that DS would be the exactly the same.
I just didn't let on that we had to travel some way, to a school uniform shop, that went up to a 36" inch elasticated waist! And beyond☺️ I certainly didn't want my DS to become as paranoid as DB at that age (who was also the same size at that age). All our old jeans were taken up by his DS (me, but yet another thing never acknowledged by 'her') for my DB to wear, when he was little. 'She' made me. I didn't want a paranoid DS. I knew, without doubt, that eventually he'd outgrow his very stocky body, just as my DB had. I could see how these people had all made DB totally paranoid about every single calorie that went into his mouth ever since!
When my DS switched schools around age 7, the weight began to fall off slowly. They allowed their children to play on the grass too, unlike the previous school. He gradually slimmed down, bit, by bit. He definitely isn't paranoid in any sense. He jokes about it, but it's no big deal to him, thank goodness.
I had to buy him jeans the other day, although he's at uni and can't afford to pay for them. Plus, I wanted to make sure I didn't hand him over a wadge, and not have it spent on much needed jeans😉.
So to all those horrible, wicked and really unkind, setting such wonderful examples on 'how to not get friends' women (soz, but they ain't 'darling' mother's in my eyes, these days) my son is now aged 21. Oh, and btw, he has a 28-30 inch waist and is 6'2", and many 'real' friends! DD, is 5'10" has a 24" waist and is very slim. Much to the shock of those 'mother's!
I bet that there are many children in your school's year, wear age sizes bigger than them, in everything, because generally most adults are taller than their forebears.