Also, at your latest post, the zombies are more a distraction for herself, they're apparently her coping mechanism for the post-apocalyptic world. IIRC it's said ones her boyfriend, and the other her ex-husband.
I think it makes perfect sense, another way to put it is, using lab equipment;
- - A bowl(you) full of water(blood)
- [The initial outbreak was airborne] - Red dye
- [When inhaled it affects the blood stream] - Add a few droplets of Red Dye to the water making it pink-ish.
- - Now everyone has pink-ish water (Tainted blood stream)
- [A reason for it now taking over instantly could be that the heart is still creating/pumping enough untainted blood to to cancel out any more infection breathed in, this would be why the dead come back, because the heart has stop 'cleasning' the blood system.
- [Now if a person is scratched or biten their skin is broken and veins/organs/artieries are exposed. This means the airborne infection has got direct access into your blood stream]
- - This is the equilvent of adding about 5 table spoons of red dye to your already pink-ish water.
- - Given a little time to settle the whole bowl will become red water (full infected)