Krystle Campbell, the second victim to be named following the Boston bombings, was a 29-year-old restaurant manager from nearby Arlington.
Her father earlier described her as a "wonderful, wonderful girl".
It says officials at first thought Krystle had survived the blasts and that Karen had died after she was found carrying Krystle's ID.
The report says Krystle's parents were ushered into a hospital room where they found Karen lying seriously injured.
They then reported their daughter missing and later found she was among the dead.
The father of Boston bombings victim Krystle Campbell - William Campbell - has told Yahoo! News: "My daughter was the most lovable girl.
"She helped everybody, and I'm just so shocked right now. We're just devastated.
"She was a wonderful, wonderful girl. Always willing to lend a hand."
Krystle - a 29-year-old restaurant manager from Arlington, Boston - was at the finish line with her friend to take a photograph of her friend's boyfriend finish the marathon when the explosions happened.