Going all out isn't good enough for Einhart. She wants to be challenged by the Sankt Kaiser. I think she is unreasonably disappointed because Vivio has only been training for a short time, while Einhart, full of the Emperor's memories, has been training much longer even if she is younger than Vivio.

I bet Subaru or Ginga could go all out and beat her, but then she wouldn't be satisfied because it wasn't Sankt Kaiser. Einhart heard that Vivio is the Sankt Kaiser the same way that she is the Emperor, and she is obviously disappointed when it isn't the glorious rematch (that she needs to win to prove his strength) that she expected.

Right now, I have zero sympathy for Einhart's circumstances. She comes off as a spoiled brat with a jaded vision of life and unreasonable expectations. I don't doubt that she will continue to win any rematches where Vivio isn't allowed to use magic. Neither of the two are going "All Out" in the traditional Nanoha sense. That phrase usually results in Nanoha blowing the holy hell out of her opponent with Starlight Breaker. Vivio isn't even allowed to use her full capabilities, which are obviously less focused on the physical aspect of Strike Arts than Einhart.