A Hidden Secret (What If Contest for EternalFaith)

Hermione Granger has a secret. A secret she had kept hidden for the past seven years of her life. But that will change when she, Ron, Harry, and Ginny return to Hogwarts for their seventh year. Draco Malfoy is unable to keep his mouth shut, or refrain from insulting others he deems unworthy to the title wizard. Or in this case witch. And it this particular trait that makes Hermione completely lose it. What is this secret? And why is Hermione so desperate to keep it that way?