I read it as she was definitely infected as she was missing a toe, and as she says in #8 "Why do you think I embraced Unity." implying she choose to be infected of her own free will in order to save her daughter.

She could well have been cured instantly because if the cure was based on Persuasion's pheromone powers then it would have been released and spread into the oxygen curing everyone. This however contradicts the later panel where Hu states there is a cure and shows the police checking people's feet.
Perhaps the pheromones only spread so far and Heather was within that range, and still took off as Claire was her focus, this justifying her volunteering for Unity.