Gosh, this is really life like! The proportions are elegant, the white coat adding a certain amount of flowing nature to the subject of your sister. The serenity of her mood and pose shows that she is at peace. There's a certain strength- in a powered down nature- that's displayed as well. I would have had increased the darkness of a few of the shadows (specifically for the lower right hand corner and on the left shoulder, seeing as how its not on the lit side) and a few more folds in the coat. A little bit of contrast would have made this better, too. Would love to see more.