Psychology Test Question

Psycho TestRead this question, come up with an answer and then go to the next post for the result. This is not a trick question. It is as it reads.

A woman, while at the funeral for her own mother, met this guy whom she did not know. She thought this guy was amazing! She fell in love with him right there, but never asked for his number and could not find him later.

A few days later she killed her sister.

Question: What is her motive in killing her sister? (Give this some thought before you answer).