It really boils down to this: “Or would it be worse if she retakes and gets a slightly higher essay score but her 1590 goes down?” Yes, it would be worse. She might receive a 1570 or 1580, which would be no harm, but it seems like an iffy bet to risk such an incredible SAT score. Her 5’s are not going to be that out of the norm. Some schools superscore, of course, but Stanford and Berkeley are examples of colleges that do not. Stanford is a special case because it does not even recognize Score Choice. They are going to see her 5/5/5 whether she repeats or not. If you were an admission officer, what would you think about a 1590 student who decides to retest? It certainly seems that she has more than enough to show that the Essay score does not define her. I would sit tight on the SAT and concentrate on Subject Tests, grades, and all of the other things she enjoys doing.