I can accept that it's an alternate universe with different rules, but if zombies existed, wouldn't they be subject to the same basic principles as other people? That zombie that was missing her legs seemed pretty worn down, wouldn't all other zombies eventually end up like that? Eventually the population is going to greatly surpass available food sources.
If you noticed, the half-zombie was always alone whenever we saw here. I think the other zombies shunned her because she was different, so I assumed that her weary demeanor was caused by depression brought on by social isolation. The poor thing could barely even bring herself to make the effort to feast on human flesh. This is just another reminder we need to nurture a society that is kind and welcoming of all people: minorities, gays, the physically disabled, torso-only zombies, etc. The trauma of depression is too cruel to inflict on people who are different from us.