I was curious because my dd always lands open but she is very upper body, rotational, slices across the ball. Just wondering if landing closed could help. I know there are other causes/solutions, just throwing it out there.
It could be an issue, but without actually seeing video, it would be hard to tell. Some people refer to something called "meaningful coil" while others refer to "max coil". In either case there is a coiling action occurring in the rear hip just prior to swing launch. If that is in tact when launch occurs, opening the front foot a little should not be an issue. Some refer to this as "creating space". But if the opening is the result of a hitter losing the coil or uncoiling too early (bleed), it is not good. If she is swinging all upper body, then it is quite possible that she is losing coil prematurely.