Oh, another idea could be Rita Skeeter trying to write an exposé on the catalogue, but she has to go undercover as a student, maybe with polyjuice or maybe temporary age regression magic for something new.

Obviously she'd have to list herself for sale so she could get her hands on a copy. She could flippantly put down something random for her listing blurb, but then be surprised when she finds that it was a subconscious fantasy she had been repressing. Maybe she'd end up succumbing to the temptations of it all after getting hit with the hormones that come from temporarily being a teen again. I think there could be some interesting dynamics if she reverted back to her true form before or during her cooking.

Another possibility is making it more dubcon and our protagonists end up agreeing to finish snuffing her to protect the catalogue from too much attention.