Jace did not relent, did not stop to give her time to breathe. The enemy wouldn't, and neither would he. He also, at one point- was the enemy. The Sith Knight showed in him sometimes. Not in the way he talked, held himself, or was in the force- he was a complete 180 of the man he was.
But it still showed sometimes. Like in fights. He pressed into her guard, poking, prodding, finding gaps. But a feint here, and a feint there. His right hand held the blade. His left shoulder came up only slightly, and-
A haymaker went flying towards the side of her head. He'd hoped to press her bladework and make her forget that the entire body was a weapon, not just the tool in their hands. It was a savage, brutal strike- much like their enemy would use, and other forms of martial arts and bladeworks incorporated. Mandalorian melee combat, for example, used many holds, strikes, and tosses to gain an edge over their opponent.
It was cruel, it was brutal, it was fast, and it might've hurt if she didn't move her head in time- but all lessons for combat were earned in blood. It was much of Jace trying to win as it was trying to teach her.