So much for that parallel birth idea from earlier in the thread.
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?