Trick question ?

[John E]

Read this question and see if you can come up with an answer. It's not a trick question. The question is exactly as it reads. No one I know has managed to get it right.

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 so that she fell in love with him right there and then but never asked for his number and could not find him. A few days later she killed her own sister.

Question: What is her motive for killing her sister?

[Edit...] Question has been answered - so think about it yourself, before reading the replies....