Nita doesn't know how to picture the Center without Emma. She was there almost an entire year before Emma arrived, but she only vaguely remembers it. She ate, and slept, and did her courses with Teacher, and practiced her "witch powers" whenever someone insisted. She wasn't very good at them.
Her family didn't visit.
But then Emma came, and she could speak Spanish, and she missed her family too, and she never pushed, never pried. And it's been three years now and now Emma's been her roommate the whole time, like the older sister she never had and yet somehow still younger than her in many ways. (She can be so adorably naive- Nita's stories of Linear life still sometimes make Emma's eyes bug out, which Nita will never admit is hysterical). They gossip about boys, out loud and telepathically; Nita wakes Emma up from her nightmares about the future and Emma wakes Nita up from nightmares about her family; Nita braids Emma's hair telekinetically and Emma helps Nita write letters to her siblings. Emma's not the family she grew up with, but she's as close as Nita has in this ridiculous place, and it is therefore Nita's opinion that they must make an Acceptably Large Fuss on Nita's 18th birthday.
Because that's what you do, for birthdays. It's important.
She tries and fails to make it a surprise; she wants to go out of the Center, Emma's only seen the stupid, glitzy parts of Jerhattan and that barely counts, and this means more organization than she can manage secretly. Her explanation for wanting to go out gets her a horrified look from the other students at the Center before she explains exasperatedly that she didn't mean a Linear, she's not dumb, she just wants to go to the mall or something for one of those fancy ice cream sundae concoctions. This idea proves much more popular. So it is that the Saturday after Emma's 18th birthday, they go out to the confectionary store in the mall, and Nita is so excited. Birthday ice cream!
"Emmaaaaa come on come on come on, pick a dessert!" she urges, grinning hugely.