It's a dumb girl who wanted to wear a shirt-vest and short hair combo but didn't want to be something as passé as plain lesbian, so called herself non-binary.

She was attacked in the girls' bathroom and the rule in that school district is you go to the bathroom of your sex assigned at birth. Nex is her gender ambiguous make-believe name, it's been scrubbed from the easily searched internet because we live in a dystopian hellhole, but some places accidentally reported her original name initially and I believe it was just a normal girl's name.