I found out that Ella was only stalking Leon because it was Kayla's idea. Kayla told her that if she didn't, things would get even worse for her at the academy. And since Ella wanted to finish her education and land a proper job, she went along with it.
Ella insisted she didn't want to stalk Leon. But if she did it, Kayla would leave her alone, so she complied. In one of her stalking sessions, though, she saw something she definitely wasn't supposed to. She caught me and Leon having sex behind the gym.
"I-I never wanted to know something like that, I swear..." she said with a sob.
Kayla, though... she was a complete bitch through and through. She didn't just shove her superiority down on those below her; she was willing to cross any line, commit any crime, just to get what she wanted. Her cruelty knew no bounds, and she reveled in the power she had over people like Ella.