i thought her teet were yellow because she was sick to be honest, like Glen but she has a higher resistance to that flu, like Hershel. She was out in the field longer than them with walkers as pets for at least 10 months in constant contact with them, she had to be exposed but has built up an immunity from it. Remember last year when Andrea was sick with the flu? Michonne was fine then and got Andrea medicine and the Govs crew nursed her back to health.
matter of fact Milton was running all types of test on people there, without a doubt someone from Woodbury is a carrier of that sickness.