I wouldn't say she needs servile pets, she needs the monsterfied subjects to grow stronger for her plan to work but if she thinks someone threatens that plan she'll kill them. See it as some kind of twisted Darwinian evolution puppeteered by Ella and in Jake's case, he was useless as a subject until she manipulated him to into growing a semblance of a backbone to get what she wanted from Daryl.how does any of this translate into her needing servile pets and killing them when they get too strong?