I'm pretty sure megaman's Upsmash will beat it, also, keep in mind that she can't jump out of the flip till it's finished. Also, it's actually very laggy if you block the footstool or if she uses the kick at all. Keep in mind, that if you block and she footstools off your shield, she can't do anything at all other than drift during the ENTIRE animation afterwards until she lands. So you have to punish her while she's still in the air.
Now if you block the kick, then she's relatively safe and can act a lot quicker out of it, but if it misses and she lands then you can probably get an easy Fsmash with megaman, not full charged of course but it's probably doable. Also, she isn't invulnerable during the actual flip, if there are any I-frames, they are only during the initial frames, so you can attack her during the flip. In fact, I've seen her get Noferatu'd out of it, which gives robin the back grab as well because she turns around. I'm pretty sure a Shulk player with good reactions could probably back slash it as well.
So how you would go about punishing depends largely on which character you happen to be using and whether they landed the kick or bounced off your shield with the footstool. I'd recommend looking at the move in training mode to see how far she can move during the flip and how much lag there is during the footstool bounce or when she lands the kick and determine which of your characters moves would work best in either situation. It might also be good to get a friend to spam the move for you so you can test your punish options.
