Brain Teaser

I got this from a co-worker. It took me some time and several hints. Can any of you put it together?

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?