She looks to be opening up (forcing it vs letting it happen naturally) way too early, which results in her clearing her hips and not getting any brush interference.
Just curious....when you throw BP what estimated speed do you consider "slow and relative to what they see in games"?
I know we frequently see 10u pitchers in the upper 40's--lower 50s here. Having said that we also don't have many girls that can handle a 31/21 as 1st year 10u.
She looks pretty balanced in the last video. One thing I would definitely work on (that has nothing to do with your original problem) is she is not getting her back hip completely through. That is a significant source of power loss.
Just a quick guess here, but it could very well just be a timing issue. I would be interested in seeing a clip from a game if you have one. If she is getting her head in front of her belly button you will get this. You won't see this on the tee. I also agree with what the ones above posted .
Ken hit the nail on the head in his post. I do not subscribe to the step to third idea. Swing mechanics should be the same regardless of pitch location. Point of contact is the only difference. As Ken said for them to expect the inside pitch and slow the load if it doesn't come. More in front...