Everyone is exposed to carcinogens daily. If you take a shower, bath, brush your teeth, wash your hair, cook with non sitck pans, brown meat, eat processed foods, breath and the list can go on for miles. These all contain cancer producing agents. All though not all will be affected by it. The risk is there.
As far as your mothers health, DO not worry until you are told to. If the test shows conclusive for cancer then have your mom get cancer smart! SHe should read everything that is out there. She is in control of any treatments. She has the final say. She should never take the doctors word as Gosple. If a diagnosis of lung cancer is found then make sure she knows the type of cancer she has. Then she must read up on how the treatments given for this specific type respond with the cancer. It is well known that chemo does nothing for lung, breast and colon cancers. The only thing found is that the chemo may give her longer but not a cure. Most cancer coughs come abruptly. And can go away. But just because she has a cough doesn't mean she has cancer. She could have been exposed to a known or unknown irritant that caused this cough. Like I said untill you are told it's cancer don't worry.