i have a question..... like a question from a csi agent.... can you answer it

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got it from the mail and i just want to know how many here can get the right answer Read this question, come up with an answer, and then scroll down to the bottom for the result. This is not a trick question. It is as it reads. A woman, while at the funeral of her own mother, met a guy whom she did not know. She thought this guy was amazing. She believed him to be her dream guy so much, 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 for killing her sister? please expalin your answer.... good day