Quick quiz

This is not a trick.
All the information you need is provided in the four sentences below.
No one I know has gotten it right, including me.

A woman, while at the funeral of her mother, met this guy whom she did not know.
She thought the guy was amazing, her dream man!
She fell in love with him instantly, but never asked for his phone number and could not find him after the funeral.
A few days later she killed her sister.

Question: What is her motive in killing her sister?