I also teach bikeability at schools in croydon. Majority of schools want children to ride as it goes well with their green policies. Maybe you could mention this. Lots of councils even offer cash for bike sheds.
Some high schools refuse to let kids ride if they haven’t attained bikeability level 2. If this is the case , get her on a course. Most councils subsidise lessons. eg. Anyone who lives or works in croydon is entitled to 4 hours free 121 tuition.
In reality what can they do if you ride to school and lock her bike up in the school car park with a descent lock. Not much.