Ozra was strong. Just like Zach, she completely ignored the norm of most summoners being significantly weaker than their familiars. If anything, she seemed stronger than her familiars, at least the metal skeleton one.
Yanael and Mandra did not want him to fight her on his own. But they didn't have much choice in the matter. Both Ozra and her Metaleton were strong enough that they could decide that for them.
Yanael and Mandra could only grit their teeth and focus on the skeleton in front of them. If they could beat it, they could help Zach.
A little bit away from them, Zach rubbed his back with an expression of discomfort. That kick had made it clear.
Ozra might be his senior and someone talented enough for the principal to want to have her as his disciple.