Well, if this girl IS Rick's kid, then it could follow that she's human. The question is whether the kid in the Governor's city will be human.
If yes, then somehow infection was a one-time thing and not carried to the next generation.
If no, Rick--and presumably Carl and the baby, and possibly Herschel--seem to be immune. But didn't one of Herschel's sons turn, implying no immunity?
Still not getting why you think the girl in town would give birth to something "not human"? Everyone is infected. If you die you turn. Unless the baby is stillborn I don't see the issue.
Making people immune is a story telling copout. This show isn't about the "one fated to save the world", it's about regular people trying to survive under horrific circumstances and how they cope with it.
I think it's pretty obvious with this past episode that no one is safe.