Atonement question??

yes i agree with the first answer, i think she fell in love with him because he was really sweet to her, and when she saw him showing affection to Cecilia she got jealous.. also she had a very imaginative mind, almost supernatural.. and she saw things that weren't really there..she imagined that Robbie was going to Cecilia or something like that, mixed with her feelings for him made her do what she did.. idk, it was kind of confusing for me too..