Nia's older siblings do not get spots in the Scholomance because they moved to the UK after they were born and died before their citizenship applications could come through. Nia was born juuuust after her parents counted as "settled", so she's in, and so are her little siblings, so they get in. Apparently her parents were trying to move earlier and this was hard for some reason.

Nia has an accent in English in spite of having lived in London all her life, because her parents assume she'll pick it up ambiently (she does, mostly) and send her to a Spanish immersion school and speak Swahili at home. The accent won't be a problem, she can read all right and it's not like everyone has to speak RP to make a spell go off.

Her parents aren't that rich and they have a lot of kids to outfit so Nia has useful items from Boots and B&Q and plenty of clothes and a light-up box for keeping any good books she encounters happy and some lab grown sapphires for storage. Nothing magical. It's okay, she can make magical things in school.

Something bursts in through the window, wisps of her mum's ward clinging to its spines, and lunges for her. Nia barely has enough time to hope it doesn't get any of her siblings before the Scholomance seizes her out of its path.