I also wonder if coaches that have told her to hold that palm up/down longer have caused an issue too.
Your are correct. Roughly palm up palm down at contact then use the idea of "throw the top hand past the bottom hand" after that to a nice full finish.
Look at the swings above to see what I mean and then try that yourself and have your DD try it.
If you maintain palm up palm down or the hitter's "box" too long you end up chicken-winging rather than swinging.