I'm not saying she's guilty. I'm saying she knew exactly what she did and she took a pic of her trophy after she did it. I'm saying she enjoyed it. The fact that she left is either because of:
A. She thought she did wrong and wanted to beat feet
B. She really didn't give a shit about the guy she just killed so she left.
Frankly I believe the answer is 'B'.
Unless you are a mind reader this is pure speculation and it doesn't make a lot of sense with the evidence given.