She is a class above the rest in artistry, so she wasn't that much overscored in PCS.
Miyahara meanwhile was overscored because the technical delegate only gave her one under rotation, even though she really looked fishy on many jumps. Kostner, while falling once and sometimes sloppy, at least rotated well.
Sotskova, Nagasu and Tennell got dinged big time for URs for example (all losing around 10 points in post performance reviews!). That's why Miyahara was overscored, she URed as much as those 3.
P.S. I've read a rumor (or maybe it wasn't rumor) that Japanese had a head tech delegate.