scooter

i have a riddle for you... a pretty simple one really.

once upon a time there was a girl. one night this poor girl's mother died unexpectedly in her sleep. while at the funeral of her own mother, this girl met a guy whom she did not know. she thought this guy was amazing-- even in the midst of her grief she fell in love with him immediately. however, she never asked for his name or number and afterward could not find anyone who knew who he was.

a few days later the girl killed her own sister.

why?