Two issues:

1) The red t-shirt of the man in the background, as well as the bright lights on the wall, take attention away from the model. I would try to desaturate or darken these elements a bit.
2) Eye contact with the model is incomplete because one eye is covered by hair. The attraction of the viewer to the model would be stronger if both eyes could be seen clearly.

The off-center composition and head pose looks good!

I agree with the above comment about the red.
Red will take precedence in a shot like this as it is the strongest color. Maybe just a slight de saturation on the image could remedy that issue.

I agree about the composition and the pose.
I disagree on the eyes comment myself as it adds a bit of mystery to the model, but that is my opinion.

Guido and Mike, thanks for your comments. I added a new one with some selective saturation:
www.vazaar.com/user:sfkp/photos/id:33047/

About the eyes, I like right one covered, she looks a bit dark and mysterieus this way. I like this pic in general becouse it's just the way my little sister is. Or, like wrote in the description of this topic: "really bring out the unique character of the subject".

I have stayed away from this discussion, not sure why, but here goes:

Having met your sister, how be it briefly, I find this to be a very nice portrait of her. She has that same look on her face that I remember. I am not particularly bothered by the guy in the red shirt or her hair over her eye. If anything I would take this version and just do a graduated lowering of the saturation and value towards the upper left.

The other version is not pleasing to me. The selective saturation is, imo, not the answer. And your other treatment did something weird to her cheeks??

Hope this makes sense and helps, anyway, cheers!! And say hi to you sis and mom for me!!

I agree with the eye issue. Its patially covered and at first glance looks like the subject is winking.

no feeling in her face!

Thank you all for your comments. For this one, I didn't ask the model for sitting nice and still and smile, but I waited for the right moment: she was reading a restaurant's menu and I waited for the moment she would rise her head. It worked really well and exept for that red shirt and lights on the left I'm proud on the result.

@ kombizz: kind a funny you say about no feeling... I've said before this picture shows my sister's real caracter, and she hardly shows her feelings at any time, like I said: she is a mystery. However, imo she actually does show some expression only you can interpret it into many ways.

@ Apurva: I don't know what you mean, do you agree it's a shame her right eye is covered, or do you think it adds something special?