Are you a serial killer?

Okay. Read the following short story thing and answer the question. This same quiz was given to convicted Serial Killers. At the end, type in what you think the answer to the question is...okay? Here we go:

A girl was attending her father's funeral. While she was there, she met the most handsome, funny, apparently rich guy she'd ever met. They talked for hours, and the girl fell madly in love with him. After the funeral, the girl realized that she had never learned the guy's name. The next day, she murdered her sister.
Why did she do it? Be specific.