I'm really conflicting about this.
On one hand, she really struggled to managed to beat him. He kept toying with her, and that's what gave her the opportunity to get used to the new body in combat, which is a good way to speed things up without being forced.
On the other hand, it's still the body of a child nonetheless. It doesn't matter how used she gets to the new body, the most it can do is the peak of what a child that age can accomplish. Unless she was capable of channeling magic, she should not have been able to deflect a magic attack with skill alone, especially not one from her previous life, when, as a highly trained adult man, he had failed to defeat that very same vampire - the one that took his life, at that!
This conflict should have been much later in the narrative, not this close to the start (which, let's be real here, it's not even the start proper). This should have been a really small fry for her to take on as the first step towards becoming the Sword Saint she was in her previous life, not the vengeance arc where she kills the evil that killed her in her when she was the strongest human alive!