Harry Potter and the Half-Blood Prince Katie Bell (Georgina Leonidas)

Poor Katie Bell: she ends up in the hospital after being bewitched into trying to deliver a cursed necklace to Dumbledore. It could have been worse, though: according to Snape, the necklace could have killed her.

After some time with the magical docs, though, she returns to school. She doesn't remember who gave her the necklace (though Harry suspects it was Malfoy, natch).