I have the SAME problem! I don't know exactly what it is but my pediatrician said it may be varicose veins and to go to a pediatrist for more info. Sorry I couldn't help but this sounds identical to my foot problems only mine have started to hurt like when I stand for a while.
Hello,
I cannot confirm a diagnosis without examination,but it can be foot blisters or fibromas.
When a foot is hot and sweaty, the sock sticks to the foot. The sock and foot then rub against each other and the inside of the shoe causing blisters to appear.Plantar fibromas are firm, nodular masses which occur as a single mass or in clusters on the arches of the foot.
Wear shoes that fit properly and keep feet as dry as possible.Wearing wet shoes, boots and socks will increase your chance of developing blisters.So change socks regularly.
And use foot powder to help keep your feet dry.If the blisters still persist then pls get it evaluated from a dermatologist/podiatrist.
Hope it helps. Take care and pls do keep me posted on how your daughter is doing or if you have any additional queries.Kind regards.