If you cook over a wood fire, directly or your smoke your meats, it's not going to inject your body with cancer causing carcinogens anymore than breathing the air around you will. Vehicle exhaust, industrial pollutants, camp fires or in your fireplace, all have some level of something bad for you in them. There's no way to avoid all possible dangers. And you shouldn't have to. I remember my grandmother telling me about growing up in the hills of West Virginia. The foods they ate, the way they prepared them and the lack of "sanitation" available to them. Not a one of them got food poisoning or seriously ill from any of that. They cooked on the wood stove, the fireplace, out back in the fire pit. Used a pig's tail to grease the skillet, ate meats that weren't refrigerated (she was born in 1911, btw). And lived to be nearly 80.
You know what got her? Throat cancer from smoking for nearly 65 years.
I dunno, I've been eating smoked foods for as long as I can remember (only been cooking them for around 10 or so), but I feel it's a healthier way to eat to be honest. Most all of the fat is rendered off of the meats so there's less to ingest. Most of the seasonings I use are fresh, no MSG, very little salt. And the taste....oh the taste. You can't beat a good rack of hickory smoked spare ribs when they're seasoned up just so.
If she's concerned about cancer from BBQ, I dunno what else to say.....gopher it! You only live once. ;)