my theories on Lizzy being sick, are neither preggers or infected, she was either:

i) in shock, she had been recently zapped by a tazer, kidnapped then nearly raped

or

ii) kalani mentioned something in chaptor 11 p2 about the 'other tower' occupants getting nauseous in a particular part of town (ground zero), near to where the first unique creatures where encountered. Kalani was also ill for a while (but that may have been a show to avoid being picked for enterainment in the arena)