Suffers from SD syndrome
I think we can summarise all these comments about her face by saying she suffers from Shannon Doherty syndrome. Hot but asymmetrical. In fact, they both have their left eye a good centimeter above their right one.
Edit: I think the asymmetry of Kat's mouth is due to some kind of jaw misalignment, which can be corrected with braces and orthodontic surgery. I had a friend whose jaw was knocked right out of place after a brawl. The doctor twisted and cracked it back into place. (Ouch.)