After she brings her hands together I think I see her pick up her right foot off the pitching plate, then put it back on....which I believe is illegal. But.... way too slight to pick up on in "real time'. She could be sliding it over a little.
It "appear"s she might be replanting after the stride, but after watching it a few times I thinks she's okay.
From my perspective & knowledge, if she's doing anything illegal it is very slight and too fine to pick up in actual game speed.
I'd be more worried about the 1st base coach standing there with his hands in his pockets.
What she is doing (my opinion) is follow through technique some girls are taught for helping with the follow through on a peel drop pitch.
My daughter did this at first to help pull up on seems and turn hand, then slap thigh with palm. It was just to help with the follow through of her pitch. She no longer does nor did she ever do it in a game, only during practice.
From the video posted I cant see anything blatently illegal. As for replant, as I have posted before ASA came out with a clarification a couple of years ago that as long as the pivot foot drags away there is no rule about it bearing weight again (replanting). I believe they refered to it as a crow drag or push drag push, something along those lines.
Her push foot does come off the ground a little but if the dirt is dug-out a little then they usually won't call it. If it's flat then it could definitely be called illegal.