My critique is not on pixel art but your use of reference.
There is a term in art called "being a slave to reference" which I think applies here.
What is the point of outlining and copying the reference pixel by pixel? If you want an exact likeness just take a picture with a camera and hand her the picture.
The idea of reference is to make sure your drawing something correctly, not to copy it line for line.
I wanted to say a bunch more on this but I forgot most of what I was going to say
so instead I will just show you what I did.
correct use of reference:No outlining, this was all freehand. Its not exactly the girl in the picture but its close enough, and I added some stuff obviously.
Some basic critiques about your version:
1. The cheek is way too puffy.
2. The lower jaw hangs down too far.
Oh yes, now I remember something I was going to say about outlining. Really, its not as useful as you might think. Thats because the pictures are not made of real lines, its made of color variations, so you won't be 100% correct when you outline, no matter how carefully you do it. So the result will be somewhat distorted, even though you outlined it. In the end you will have to hand-correct it to make it look right anyway.