I think sketching some reference lines for yourself would help. Generally the mouth line is parallel to the eye line. In your image it is unclear how much the head is tilted to the side, that is, towards/away from the viewer. The eyes tilt, but the mouth is horizontal.
Compare these two images. Eh, not a great reference, but it was the first I found.
The first is a fairly level 3/4 view. The eyes are level. The mouth, corner to corner, is roughly parallel, although the expression makes this hard to see. The second image is the same model, 3/4 view, with a tilted head. Mouth remains parallel to the eye line. Neither has the head tilted back (chin thrust out) like your image, and the face is structured differently (this model has a weird compressed face), but hopefully it helps with the angle of the mouth.
Also, consider moving the entire mouth down a pixel and making the upper lip a straight line (at whatever angle is correct). A big smile tends to straighten the upper lip, unless the view is from under the chin.
Issue 2, the hair. Your friend has thick curly hair. It occupies volume, and rises above her skull. In your image the hair is painted on the skull, and looks almost straight. I don't have any specific fixes because I'm terrible at hair, but I see the problem.
Good luck,
Tourist