Well I'm not really sure how that'd be done differently. We know Sakura's been training under Tsunade largely off-panel, we know she's got monster strength (see: Sasori fight), and I think the nature of the move she used in this chapter is pretty in keeping with that progression. Silently storing vast quantities of chakra in order to use it all at once is Tsunade's trump card, and Sakura's greatest skill was always chakra moulding. It's not like there's even any proper "training" to show for a move like that.
Acting like nothing ever happened? When he showed up everyone was like hey you piece of shit where do you get off showing up here and expecting us to just be best buds. They were ready to fight him at first. They're in the middle of a battlefield, though, some of this shit has to just be put aside so they can work together against the things trying to kill them. No one forgot what he did, but the only thing that matters right now is that he's not going to try to attack them, and he's going to help them. The rest can all be put off and be dealt with later.
Now Naruto and Sakura definitely don't react like that. Naruto is in keeping with his character, so I have no complaints. Sakura I think has just always wanted things to go back to how they used to be. Yeah she tried to kill him, but she failed miserably because she couldn't bring herself to do it. However much she SAYS that she's done with Sasuke, she's never actually been. And now here he is, and he's acting friendly, and it's gonna be extremely hard to not be allured by that in the moment. NO ONE in this situation is just all best friends again, but the nature of the battlefield is forcing people to make abbreviated judgements and just roll with them so they can get things done.
[Edit] Man, everyone already said all of this while I was typing!!!