I suppose it could be said that the most important thing with any image is whether you
like it yourself and maybe in the case of a photo requested by another whether they like
it.
I like your image but I can’t help thinking that I would have liked it more if the your niece
had eye contact with the camera and maybe a smile.
I can’t talk as I never smile when a camera is pointed in my direction.
My guess is the ‘young lady’ wanted to show off the hair-do and hair piece. I wonder if maybe she is looking off to the distance just a tad bit much. She looks like she has amazing eyes, maybe try it in colour?
I agree with Sirvad, I think a little more kick, but I don’t know if you can adjust the contrast levels with the white dress? The softness kind of suits your niece too.
I’m sure she’ll love it, she looks ever so grown up like your title suggests.