"Hi!" a voice suddenly called out from down the alleyway. Yelping and blushing brightly, Gaz spun around to face the speaker, sputtering a desperate explanation for her situation, only to calm down as she saw who it was.
"Oh, it's you," she said flatly, seeing GIR in his dog costume, licking an ice cream cone, "What are you doing here?"
"Umm, I forget!" the dimwitted robot said cheerfully, before he started laughing and pointing at her, "Heehee! You're naked!"
"Shut it, you little-!" Gaz growled, blushing again only to trail off as her last word made it occur to her that GIR wasn't actually that much smaller than her. It might be a stretch, but that costume just might fit her. But how to get it?
"Hmm," she muttered, before smirking and saying, "Yeah, I am. And it's pretty fun. You should try it."
For a minute, GIR just stared blankly at her in response. Fortunately, just as she was starting to think he hadn't understood a word she'd said, he grinned widely. Dropping his ice cream, he quickly unzipped his costume and jumped out of it with a flourish.
"Feel the wind!" he yelled with a laugh, quickly running off out of the alleyway and disappearing from sight. Gaz watched him go, before sighing with relief, dropping the trash can lids she was using as makeshift cover, and picking up the discarded costume. As she thought, it was slightly too small to comfortably fit her, but with a little shifting and struggling, she was able to get it on. The end result left her feeling stiff and made movement a little hard, but it was much better than the alternative. As an afterthought, she also slipped the dog head hood on to hide her face; she didn't want anyone recognizing her and questioning why she was walking around in a too-small dog costume.
"Now to just get home, get my real clothes back, and beat up Dib for causing this," she said to herself as she started walking out of the alleyway.
Unfortunately for Gaz, she wouldn't be getting home anytime soon, for shortly after reaching the street...
Option 1: She's mistaken for a real dog and captured by dog catchers.
Option 2: An enemy of Zim's (other than Dib) mistakes her for the real GIR and attacks her.
Option 3: The teleportation spell suddenly kicks in again and sends her somewhere else, leaving the dog costume behind.