This sort of thing gives me The Rage!
We have had such issues with DD2's school shoes (senior school).
Last year she wanted Kickers - the lace up ankle boots. They are barely boots. So, we bought them, thinking they are good for walking to and from school, comfortable, practical for lessons such as art, DT and the sciences, where some protection may be needed.
The HOY contacted us to say they weren't allowed. I pointed out that a year or so earlier, the head had said she couldn't dictate what kind of shoes could be worn, aside from the stipulation of "flat black shoes". The HOY told me they were fashion shoes, and that they were not black, because they had the green and red branding. I said I would remove the tags, or colour them with indelible marker. She agreed to this.
Then one of the deputy heads got involved. She said they were boots, not shoes. Disputable, but I accepted this, and bought Kicker shoes. They did everything the boots did, but were slightly lower on the ankle. I was not asked to colour in the branding tags.
This year, DD2 chose similar shoes to last year. They are Ricosta shoes, and from the "boys" range. They are marketed as school shoes, and if a boy wore them to school, no one would bat an eye lid. The HOY has told her she thinks they are a bit too much like trainers (they're not, except they fasten with Velcro) but has magnanimously allowed her to wear them.
I have had children at the school for about 10 years, and during that time, girls have always been allowed to wear ballet flats, which are impractical on almost all levels, and frowned at by podiatrists for being bad for feet, particularly growing feet (they stay on by being too small). You can't easily run in them, so they don't encourage exercise, they are not hard wearing and they afford little protection from droppages.
Oh, they are feminine, though! Could this be the reason they are acceptable to be school, and DD2's "boys" shoes are not?