Period underwear for tiny 10 year old

[LadyGAgain]

Hi!
As per title. She's so slim hipped. I just bought her Asda size 6-7 shorts and she's 10.
She's having cramps and moods and perhaps periods are round the corner. I want to support her and tampons or towels in year 5 isn't what she wants.
Please can someone share their experience and wisdom as she's my first.
Thank you,

Hey, no advice as my 12yr old hasn’t started yet but following for any advice as she is also very petite & her underwear is 7-8years currently

We had some pretty tiny XS ones from Modibodi but maybe not that tiny.