The way Darwin sees it, in addition to Uhura's company and her willingness to share her considerable stash of makeup, there are certain perks to her joining the women in Carol's quarters when they get together.
The first night had been a bit awkward. When she arrives, they are a few drinks in and happily abusing Kirk, as Christine, newly returned to the ship, cheerfully recounts what amounted to a truly horrible one night stand. "And so after that, I just can't, and I get up to leave, and Kirk's just sitting there, naked-" Christine's on a roll when the doors slide open and Uhura stands there uncertainly, backed by the light in the corridor.
As Assistant Chief Science Officer (a title that always made Carol snort in that upper class British way and lament that with Spock's work hours, it was a miracle there was any assisting left to do), Carol has the biggest quarters of any of them. Still, they aren't large and Uhura can certainly hear the topic in question as she steps in the room.
"Kirk?" Uhura asks, taking the seat Rand vacated for her. Rand squirms on Carol's bunk between Hannity, Madeline, and Jodi, all four leaning their backs against the bulkhead and messing up the quilt in a way that Darwin is sure drove Carol nuts.
"Sorry," says Carol quickly, directed at Uhura. "We didn't mean- I know he's your friend."
Uhura sits primly on the edge of her seat and looked at all of them. Darwin had a sudden, sinking sensation that Carol's impulsive invitation that afternoon had been a mistake. Drinking isn't strictly forbidden on board, but Hannity has a shift in a few hours and Carol is on call in the morning. None of them knew Uhura well, since she was clearly one of the boys on the bridge, as they called them. She ate with Kirk, McCoy, and Spock in the mess hall, and went running on the treadmill next to Sulu in the gym, and perhaps that wasn't a line ready to be crossed. But Uhura smiles, looked down at her lap, and then back up at Carol, then Christine.
"I'd love to hear about Kirk," she says. "I'll tell you about the time he was in his boxers under my roommates' bed at the Academy." She reaches down beside her and pulls out a bottle Darwin hadn't noticed her carry in. "I brought wine. I didn't know…" she pauses and looks at them again. Darwin often thinks of Uhura as one of the boys, invited to their poker games and spending shore leave with the other senior officers, but maybe not. Maybe, Darwin thinks, she's lonely, up there at the top. "Don't tell the first officer," she says with another smile and ducks her head, clearly embarrassed.
And she becomes one of them with that, since out in the black of space, the other crew members were all they had and on a ship like the Enterprise, women are far and few between.