Flat feet

[Longdistance]

My dd11 has what I believe are flat feet. Her shoes fit her oddly in that where her arches should be, the shoe protrudes out. Her feet are a size 4 and when she runs her feet flap around. Dd has recently had back ache too, so I’m worried this is associated with her flat feet.
I spoke to our GP in November but we are waiting for someone to see dd at the hospital.
Has anyone’s dc been through this?

I have flat feet. All my kids do too. I'm not sure if it's affected anything but I have bad knees. My dads feet are flat and he has bad knees too?

I know this is an older thread and you may have seen someone. . . but. ..
Do her arches form when she stands on tip toes? Children reach the adult foot position at about 7 so her feet are not likely to change now.
Insoles do not change foot position, only "prop up" the arch, so no longterm change.