SOz just seen your post above mine ref women's sizes.
What style of clothes does your dd like or want?
Has she got a mood board/ clothes / style wishlist? That would be a really nice activity together and never too early to look at working out her best colours to help her to find things that really flatter her.
Most kids now just want sports casual stuff. Joggers etc are way more forgiving, cargo pants are right in fashion at the moment for kids and with a nice tee and hoodie she'll be comfortable, in style and not have concerns about dresses stretching over tummy.
If she wants dresses then look at sweatshirt style dresses, again, forgiving, comfy and look great with leggings or tights and trainers. (Not knitted jumper dresses, too clingy across tummy, I speak from experience)
And t shirt style dresses for summer, nice track top jacket or hoody v fashionable, h&m or other store basic tube skirt with sweatshirt loose over waistband
Party type dresses look horrible on kids over the age of about 7 anyway. if she's conscious of her shape then she will feel crap in them and look ungainly. Bless her.
I know you havent asked for tips re weightloss but I have disabilities so really struggle with we, Does she have a sport or enjoy swimming?
swimming is a fun low impact exercise you could do together, make it fun for her without ever mentioning weight or exercise.
A friends child was having difficulty with weight, and really couldnt curb his eating.
I don't think it'd helpful for kids to 'diet' it can set them up for a life of disordered eating and yoyo weight changes.
his mum drove him everywhere but after lockdown couldn't manage work and school run so got him a bike, the weight fell off in no time and has never gone back on.
granted he's a bit older but your dd is young enough for you to suppport by stealth.. scooting, cycling or skateboarding is great fun, and regular walks, borrow a dog if you don't have one, but don't make it about weight, just about fun and give lots of praise and by the summer she'll be buying clothes for her age wherever she wants