6th graders Lateral thinking

There were once two sisters whose mother died. Let's call them Anna and Elsa.
The day of the funeral, among the people who were at the cemetery, there was a very good-looking young man, and Anna fell in love with him. Ten days later, she killed Elsa. Why?

Courtesy of Laura M. First right answer gets a little treat on Tuesday. No Google, please.

Love,

Laura