Well, CFD is pretty clearly inspired by some of the classic horror movies of days gone by. Invasion of the Body Snatchers, Stepford Wives, The Thing, The Faculty... There are countless tales of people being replaced by something... Other to draw on. And in all these tales, a common element is that it is hard to tell who is still the person they claim to be, especially when the chips are down and everything is on the line. Pressure and adrenaline push our 'fight or flight' reflexes into high gear, but deaden the whole 'logical thinking' and 'normal behavior' things. So someone displaying abnormal behavior or a short temper may just be feeling the pressure, or that could be the first sign that they've changed. Which only increases the pressure on everyone else, and so on.
Until we see Butch making serious out of character moves (such as when Riser abandoned his old MO to go for big explosions, or when Fastjack started posting Horizon spam) then we ought to watch carefully, but assume she's unaffected. Much the same as with any doctor who has been treating patients with an infectious disease, but hasn't shown symptoms of contracting the disease yet.