So long and Thanks for all the fish

Read this question, come up with an answer, and then email your answer to me. This is not a trick question. It is as it reads.


A woman, while at the funeral of her own mother, met a man whom she did not know. She thought this man was amazing, the man of her dreams, so much so that she fell in love with him right there but never asked for his number and could not find him. A few days later she killed her sister.


Question: What is her motive in killing her sister?
FYI for those that haven't answered there is now right or wrong answer, atleast try and give an answer