The next time she meets up with her friends, she's grinning maniacally. "Sooo? We're going, right? Oh man, I need to find a date, don't I? And an outfit! Merlin's apples this is going to be great."
"Anyway, I found my spare," Karen says, producing a royal blue dress robe. "There's a splodge on it that will not come out, but I know what made it so if you wanted to mix up more of the same potion and turn it into a pattern you could. Or just hack it off and wear it daringly short, I don't care what happens to this robe." The splodge is a sort of periwinkle near the hem.
"I'll take the pink one! It's pretty," Jenny says rather defensively. She touches the robe, which turns into outright petting it. "Oooooh, and it's so soft."
Alli snags the royal blue from Karen and holds it up, trying to eyeball where the stain would be cut off. "It wouldn't even be that short on me, I think?" she guesses. "What do you think, guys? Too short even for me?"
Vivian quietly gets permission from Emma to collect the simpler of the two extra robes. It's a pale purple she's not convinced will look good on her but it's at least edged in a darker purple she likes better, and the other one she's pretty sure will make her skin look green. Purple it is!
Jenny sizes up Alli. "I think it'll turn out all right? You won't make the Headmistress faint, at least."
"Just don't twirl too energetically," Miranda says. She takes the last spare Emma robe, a sky blue. "This looks like it'll probably fit me."
Jenny spots Alli's contemplative expression. "You'll get thrown out sooooo fast," she points out. "Doesn't that sorta ruin the fun?"
"I am very sure I'm not better at a Stitching Spell, but I am very very good at hemming!"
"Er. It coooould be, I don't make clothes or anything? But hemming is easy, I don't even really have to think about it much."
Jenny holds the robe up against Alli and makes considering noises at the stained patch. Finally she carefully folds the edge over and then refolds the robe around it. "All right. You-" she pokes Alli, "come by tomorrow so I can double check the length, okay?"
Alli suffers the sizing up in reasonably good grace. "Yes mum, thank you mum," she says with a roll of her eyes, but the thank you sounds sincere enough.
The next afternoon, she goes down to the Quidditch pitch while the Slytherins are practicing. And if she happens to stay put until they leave and the Gryffindors show up, well, shame on her for losing track of time.