IS A PUZZLEMENT - PART I

I recently received an email with the question posed below.

.
This is not a trick question. It is as it reads.

.
Here goes -

.
A woman, while at the funeral of her mother, met a man who she did not previously know. She thought he was amazing. She believed him to be her dream partner so much that she fell in love with him right there, but never asked for his number and could not find him after the funeral. A few days later she killed her sister.

.
Question: What was her motive for killing her sister?

.
Give this some thought. I will post the answer tomorrow.

.
FYI, my longtime friend Carmen "the Bear" told me he got the answer correct.

.
TTYL