Received in an email. Perhaps you've seen it.

Read this question, come up with an answer and then scroll down to the button for the result.

This is not a trick question. It is as it reads. No one I know has gotten it right.

A woman, while at the funeral of her own mother, met a guy whom she did not know. She thought he was amazing and she fell in love with him right then and there, but for some reason never asked for his number and couldn't find him after the funeral when she looked. A few days later she killed her sister.

Question: What was her motive for killing her sister?

[Give this some thought before you answer.]