Branwen scowled at the other girl's impatience. She knew she needed to go to the loo, but she wasn't a miracle worker.
She ran through her repetoire of spells in her head, before deciding to try another revealing spell - she didn't know any other unlocking spells. "Specialis Revelio," she said clearly, tapping her wand on the door, then repeating the steps for all four walls. There was a vague glimmer of old magic that was mostly faded around the window and the door. Unfortunately, she couldn't quickly identify it.
She sat down at the desk and pulled Hogwarts: A History towards her, telling Vicky to "try anything you can come up with" as she flipped through the book, seeking something about a magical locking room. she thought she might have read something, but it was a large book, and even a Ravenclaw couldn't memorise all of it.