The mother doesn't want her to have formal education.
There are plenty of children who do very well learning organically and following their passions. Not everyone needs to undergo an industrialised education through formal schooling. There are many unschooling/home schooling examples where children do not learn to read till they are 9 or 10, learn it immediately and take off. At some point, she will want to read and at that point, I imagine that her parents will teach her.
Steiner philosophy does not encourage children to learn to read till they are 7/8 and most children suffer no ill-effects from that.
Sounds like she is in a very fortunate position of travelling widely and learning about the world. Unless the parents are genuinely neglecting her well-being, I would let this one go.