With her a cold can be very serious. She has a weak cough. She can't cough up secretions like others normally could. It can be pretty dangerous.

Stay in your boats,” Dahra said. “We’re still going to need food. Throw your fish onto the dock. I’ll get Albert to send someone here to collect it. Then go back out, row up the coast a little ways, and camp out.”
“Camp out?” Quinn echoed.
“Yes!”
“You’re serious.”
“No, it’s my idea of a joke, Quinn,” Dahra snapped. “Pookie just coughed up a lung and fell over dead. You understand what I’m saying? I mean he coughed his actual lungs out of his mouth.

I think he has serious difficulty controlling it,

She's got a deletion of a certain strand of DNA that produces survival motor neurons. Because she doesn't have that, she basically loses the connection from her nerves to her muscles and the muscles (then) atrophy.

They talk and it's been good for her. They're kind of going through some of the same things.

It can show itself later after the kids are older and are walking, and (they) slowly lose that ability. There's also an adult onset form. The earlier it manifests, the worse case it is.