Maida’s school is Catholic, but the students aren’t necessarily. I taught at a Catholic school in London for a day once where the majority of the students were Muslim. I don’t actually know how common a thing that is in 2016. But Phobos and Deimos isn’t set in 2016, so.

↓ Transcript
Panel 1: Maida: "M-Mars?"
Panel 2: Nat: "Mars, yeh? That's what I fought."
Panel 3: Thurga tugs at Maida's headscarf. Nat: "What religion are they on Mars, Thurga?" Thurga: "Mmm, some Martian religion, I fink."
Panel 4: Thurga pulls Maida's scarf off. Thurga: "Woops!" Maida: "Oi!" Nat: "Ha ha!" A teacher in red sunglasses notices them.
Panel 5: The teacher: "Kilwa! Maida Kilwa, year ten student. Your file says you're new, but by now you ought to know that O.L.P.I. is a respectable school. Members of all religions and sects cover their heads here, Miss Kilwa." Nat: "Snerk."
Panel 6: Maida plants her scarf firmly back on her head and marches away just as the bell rings. The teacher: "Nat Fisher and Thurga Ramakrishnan! Please behave 'ospitably to our alien students."