second, go back and take all that defensive stuff out of the description.. i did read it and its all not needed.. try this: "this is my sister, she is a beautiful and i am proud of her, i wanted to share this amazing shot of her with you.." i think youshould be far more secure of this piece and let it stand without any potentially defensive statement!
i can see why you are proud of her, she has a presence in front of the lens, its calm, and just on the confident side of provocation. she doesnt waver from looking, her awareness is for the one looking back, her dress or look appears quite unimportant to her.
that makes the viewer feel the same, an empathy is struck, and humanness remains.
i wish her all the very best in carrying her meassages to a wider public thru modelling.. and your image of her is a wonderful kickoff to that journey the tonality is perfect and because of right-contrast there is no loss of depth or texture. the wide open space (dual monitor i know) pushes you around, you almost 'walk' over to her side of the image to escape the empty nothingness.