To fight for the others or to wait for his own sake?
Leo rushed towards the breach of Martin's making with all the might of his legs, at the greatest speed he could… All the while carrying Mei on his back.
It was one thing for her to move around with her freshly and now mostly restored body. But sprinting down several flights of stairs, jumping out of the window roughly five meters above the ground only to then soften the fall with just knees alone before sprinting for her life towards the recently breached part of the wall…?
This kind of athletic performance was still far outside of Mei's reach.
And so, rather than lagging behind Leo and potentially getting lost in the fortress or outright encountering some sort of danger that could take her by surprise, Mei ended up carried all the way to the vital area of the staged siege atop Leo's back.