Meanwhile Ariana got there on foot. on a magical path that indulges in non-Euclidean geography to cover a great distance that its length should allow. A path, furthermore, that is magically made and maintained by humans, who can make more.
Furthermore, when they set out to visit another school, in the mountains, they take those paths.
Something's got to give.
Freight trains and magical paths are one thing. Just because they can lug their luggage doesn't mean that much larger transport would not be needed. But passenger trains are not. Unless there are complications with routes, and I don't think that would help.
But then, just about anything I described above could fix the problem by vanishing. Susan's arriving by foot. Wizards not having the power to create more paths. Their going to the school afoot. . . .
Decisions, decisions. . . .