It was fairly important to establish just how much mana she’s got now as a result of consistent training her entire lifetime to raise it. Also I think it was very important to establish that her primary tactic (which she learned from her teacher) is to prey on opponents completely underestimating her strength.

She even mentions that Aura could have beaten her if it had been a head on fight with all of her knights. But ultimately the thing that wins this fight was a very simple deception that she’s carried with her from her teacher her whole life.

And she’s passing that same deception to Fern too.

This whole arc establishes one of the more important skills passed between teacher and pupil.