That I wanted to pare down the number of characters to deal with is not an in-universe justification.
Yes, a lot of the pupils have left school for trade-related training instead. Yes, the place is far from a city. But it is not exactly a hamlet consisting of two roads. It is, in fact, a central point where a lot of people come in and go out to deal with crucial magical matters. There are enough of them living there -- as support structure, if nothing else -- to create throngs on festivities, and fill up many houses.
So -- well, the girls are easy in a world that's still steampunk or maybe a bit of dieselpunk. There's the boys' school, and then there's the girls' school.
But five girls for advanced study. . . . or perhaps, the gifted and talented group. I suppose I have to put in something where she's tested in mathematics, the only subject in which they could be sure she learned outside what they taught here, and there might be some quibbling about a girl who has to be tutored in so much just to catch up going in it, but I suspect someone will overrule all objections because they need all the -- well, they wouldn't say gifted and talented in that era. Bright group, perhaps. Or upper form. . .
I shall have to ponder the term.