(But she does conscientiously ensure that they're all done and dressed and so on sufficiently in advance of eleven for her to make her new curfew.)
The next day, Bella shows up in study hall as usual. "Hey Giles. Progress on Prom Ghost? Do the records actually go back to seventeen-thirty-two and we should split them up?"
"The article doesn't name him? Maybe there's one from a later paper after a trial that does?" Bella suggests.
"Okay. Should we split up the archives? Prom's in four weeks."
"I'm not coming after school," she calls over her shoulder as she goes, "I got invited on a dress-buying expedition, so don't assume I got eaten when I don't show."
After school, Bella goes with her school acquaintances with whom she maintains a shallow sort of friendship to purchase dresses.
To her great surprise, she finds one she really likes. It's indigo, almost the same color as her mask, and it's knee-length and twirly enough not to be too much of a hindrance if she has to physically fight the ghost. It has matching shoes with pokey heels, which she can now actually walk in given new preternatural balance, and which strap on snugly enough that she could probably stake a vampire with her footwear in this getup if the heels are wood under all the indigo lacquer.
It's not on sale, but she buys it anyway. It fits.
It's hanging near the window when Sherlock comes by for breakfast.
"Thanks!" says Bella cheerfully. "I don't usually like dresses that much, but I like this one. ...Do you need a square or some cash or something to handle your prom outfit, or are you going to bet on your usual wardrobe cutting it with the door folks?"
"I may be able to scrounge something more or less respectable," he says.
"I should probably buy tickets at school tomorrow," muses Bella.
"Giles found the likely Prom Ghost. She died in 1920, there was a live suspect - haven't found out who yet - and she was strangled and drowned both, not just one or the other. So if you meet her, we think her name is Minnie and she's pissed off 'cause her boyfriend murdered her."
"Of course, in the intervening years she's killed over sixty people, so I'm no longer particularly hopeful that she's lucid enough to be reasoned with."
"Why can't all the traditionally evil critters be more like you?" Bella asks rhetorically.
"Pity." She walks a few steps in silence, then says, "Do you have speculations as to what leads some vampires to - enter the service industry - instead of doing the sociopathic hedonism bit? Does it not occur to most of them, do you have to be in a guild or the existing bite shop employees will kill you, is it just some sort of psychological diversity much like how you're all special that is alas unbottleable...?"