Going to the party, it was already well on it's way to being over. People were already leaving or passed out and unable to move. Luckily for her, Looney Luna was still there at the refreshment table. Coming up behind the Ravenclaw, she waited until no one was around before she took out her wand and stunned the other girl.
Not bothering to catch Luna, she let the girl fall in a heap behind the table. Dragging the unconscious girl underneath the table, there was a tablecloth with long sides draped over the edges to give her privacy. Stripping Luna of her clothes, she left the blonde in nothing but her underwear and socks. Just for fun, she wrote 'slut' on the girl's stomach.
Removing her own clothes, she put on Luna's which amazing fit reasonably well. Bundling up her clothes, she transfigured them into a large mask. Donning it, she left the table and found a drunk, passed out Ravenclaw student that looked to be the same age as Emma. Helping her to her feet, she all but dragged the other girl to Ravenclaw Tower. Joining a group of other students returning from the party, no one paid them any heed as they entered just behind them.
Dropping the girl in the common room now that her purpose was served, Astoria hurried upstairs. Inquiring of a passing student in her best imitation of Luna's annoying voice, she found out where Emma's dorm was. Heading up to it, she opened the door slowly, peeking inside to see if it was safe to enter. There was one girl changing into a nightgown by her bed and three beds that had their curtains closed. Slipping inside, she saw no one else around or watching. Stunning the dressing girl, she did catch this one and eased her onto the bed. Closing the curtains, she waited and listened...