Oh, boy. I also agree with much of the criticism. And I also really feel for the artist because it is far, far, far from horrible and I am sure that he wanted to create a masterpiece given his beautiful subject. I have painted portraits and taken intensive workshops given by professionals on portraiture. It is very, very difficult, probably the most challenging thing to do in fine art.
My humble opinion, is that the issues came out of creating the smile. If you look at most painted portraits, especially museum quality, the subjects are VERY rarely smiling (and NEVER showing teeth). That's because it is so damn difficult to get right, even for the masters.
When I look at Kate's painting I absolutely see the masterly painter's technique and so much that was done beautifully, but also the problems that many are complaining about.
Also, a painting is ideally meant to be viewed from a distance, not close up, so some of the criticism, like the "gray hair" are just wrong: recessed/recession on hair is done with neutral grays.