Fear the Walking Dead (spoilers)

[ChrisIII]

She seems to think it came from the Zombie bite, which doesn't contain a virus itself technically (Every death apart from severe head trauma activates the reanimation-"We are all infected") but is toxic/fatal enough on it's own.

Maybe it is just the arm and she's kind of like Grace was in season 5, who thought she was dying of radiation poisoning when she was actually pregnant (Of course, kind of different).