Why does she kill her sister?

A young woman is attending her mother's funeral.
While there, she meets a man she has never seen before and falls in love immediately.
After the funeral she tries to find him but cannot.
Several days later she kills her sister.

Why does she kill her sister?

Click here for Answer

She killed her sister in hopes that the man would be at the funeral. Some people say this riddle is a test of a psychopath. If you answer it correctly, you could be one.