Jeff Jacques had a post on Twitter once about using the pronouns a fictional characters uses that are appropriate for the character at the stage of the story you’re writing in. That makes sense to me.

The future world Maida and Maria live in isn’t that great, but it is the future, and while I can’t promise they’ve sorted out all the gender garbage we’re surrounded by in 2018, nobody has tried to outlaw trans people in at least 450 years by their time.

↓ Transcript
Panel 1: Maida and Maria walk into the school. Maria: "That's why you've got to come here to do anyfing wiff art."
Panel 2: There is a poster on the wall for a youth musical about Sun Wukong. Maria: "Vee-ess schools are rubbish for anyfing except academics and gaming, innit?"
Panel 3: Maria: "I never joined the poetry club when I was here, but Miss Odomo is a great teacher. You'll like her." Maida: "Maria. I have a question."
Panel 4: Maida: "You're trans, right? That's the word in Yingish?"
Panel 5: Maria, shrugging: "Maybe! I don't know what I am, Maida! I'm still figuring that out."
Panel 6: Maria (sparkling): "I just know I definitely ain't a straight girl. You can keep calling me 'she/her' for now, though."
Panel 7: Maida: "Well... then... wouldn't it make more sense to go to a school like this, that's not just girls?"