Brain Teaser

Read the scenario and question, and then come up with an answer. Click on the comments section to see the solution. This is not a trick question. It is as it reads.

"A woman, while at the funeral of her own mother, met this guy whom she did not know previously. She thought this guy was amazing, so much her dream guy she believed him to be just that! She fell in love with him right there, but never asked for his 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? (Give this some thought before you answer.)