Yes, she's got one of the riding school ponies on half-loan so she's down at the stables most nights and all weekend.
She's already got jodhpur boots and chaps, but they're not great for the wet weather, mucking out etc. (We're in the North of Scotland so she needs boots for the bad cold/wind/rain/snow). Last year we put the boots + chaps away for the winter and she used the rubber long riding boots. (Although they collapsed after a few months of use). The only problem with the rubber boots is that they don't keep your feet warm.
The only other option I can see is to get some of the more expensive country-type boots that come in an extra-wide calf, but she will probably manage to destroy them in a few months, too. 
There's no option for her to change boots to ride in whilst at the stables-- so she needs boots that are sturdy enough to muck out in, but also OK for riding.
@spudlet, yes, the stirrup irons are large enough for her feet. She has her own normal stirrup irons, but it's a faff to switch them over each time she rides. The riding school will only allow people to have lessons with the caged irons.