Lol it's disturbing how many people got it "right".
The "correct" answer is she killed her sister in the hopes that the strange man would show up at the next funeral. So yes, so she could see him again.
When I answered this one for a job I said it must have been a crime of passion. She found out her sister was seeing the guy or something like that.
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*Factoid: "There are no such things as Hogg Island or Columbian boas"