Not really supposed to compare times in xc, but I took a look at the splits from nationals last year and they were in similar places at 4k at Nationals versus Nuttycombe-
Valby was 12:57 (Nats) vs 13:00 (Nutty), Tuohy 13:09 (Nats) vs 13:07 (Nutty).
The difference seems to be that Valby kicked harder at Nutty, whereas Tuohy seems to have faded a bit and kicked very late.
Valby seems to be in better shape than she was last year for sure and Tuohy has some work to do.