Boggart
DISCLAIMER: Don't own it. Plotbunny from ChoCedric at FictionAlley.
Before she had found the diary, her boggart was Harry Potter laughing at her, telling her that he would never love her, never like her, even – telling her that she was an annoying brat who did not deserve any acknowledgement.
After she had found the diary and met Tom, but before the diary was destroyed, her boggart was someone walking in on her writing in the diary and finding out her secret. In class, everyone just assumed it was a regular diary – little did they know.
And finally, after the diary was destroyed, her boggart took the shape of Tom, lying on the floor, blood dripping from a wound made from a basilisk fang, which still protruded from his chest. Even though she knew that Tom was You-Know-Who, she could not stop loving him.