Hitting form is excellent until game time

Your DD looks like an athlete. She certainly can be very good if she likes playing. Looking at the practice clip I see a player (and I see this often) who swings from the pelvis up, then pivots or rotates her hips so when she finishes it looks like she had a good cut. Look at the reverse pivot of the back foot as opposed to the attached clip below. When a player initiates the swing with the arms and upper body they tend to be late a lot (which your DD seems to be even in the practice cuts) and then they compensate by reaching out to the ball with their arms (like your game time picture).

She can hit well off of a tee because the ball is not moving. Wiffles because they slow down so much on the way there. Before you are sure it is a confidence or mental issue realize that the confidence problem may be the result of mechanics not getting results instead of the confidence issue affecting mechanics.

I would suggest a lot of front toss with real balls in a cage. That allows for a variety of pitch locations and real feedback on ball flight path after contact. Get lots of video of each session. Look at this swing below and look at the connection of hands and hips as they rotate around the corner at launch. Study the timing of the front foot and the nice rhythm created from weight transfer into launch or swing. Be patient. As her mechanics improve so will her results.

Thanks so much for your thoughts. I hope to show her the comparison and your comments tonight.... or more likely tomorrow. Golf and gymnastics practice tonight so no Internet tonight. But I'll keep you posted and we'll see what modifications she can make. I'll try to take some more video of batting practice and post.

First off, the dog is awesome! I just saw the video you posted, and this changes things a bit for me. I still suggest practicing more like a game situation. I have my DD's in their cleats, wearing their helmets and batting gloves every time they are swinging. Doesn't matter if it's wiffle balls or soft toss. However your DD seems to be suffering from a timing issue more then anything else. I think LHowser gives you some really good advice for fixing her mechanics, but I think she is SO far behind the ball you may want to address some basic timing first.

She is just landing her stride foot at the point she should almost be at point of contact with the ball. The last cut she takes, she has landed and started her forward movement before the ball even comes into frame, which was much closer to where she should be, and she made contact. I would work on some verbal cues with her. I use Ka Boom with my hitters, Ka for the stride step, and boom for the poc. I have heard four or five different ones, this is just the one I use with the younger hitters. Have her say it out loud as she swings.