Petra was a kind and caring woman who looked after and guided Eren Jaeger when he was first admitted to the squad and she seemed to have acted as some sort of attachment figure for Eren among Levi Ackermann's Squad as she was the one shown to worry about him. Although all of Levi's squad wished (and demanded, to an extent) Eren's unconditional trust, it was ultimately Petra who convinced him to do so.