While on the way to Peter's base, Mathew spent quite a while trying to figure out what was the source of the problems over there.
Because the situation appeared to be simple only on the surface.
From an outsider's perspective, Leila's actions were the most straightforward course one could take. Rather than waiting for people to turn into zombies, she did everything in her power to buy them as much time as possible so that they could survive until Mathew would arrive with the cure.
As for the people who couldn't have their wounds cleaned out, cauterized, or simply amputated, she opted to keep them separated from the rest of the group, ready to pounce on them the second they would start to turn.
It was that simple. A set of rational decisions aimed to save as many as she could while taking the necessary cost of doing so.
But…