The decision to use bear spray seems to have reduced injury, as the bear ran off after being sprayed. Would a firearm have prevailed better? Probably depends on size of bear, caliber of gun, distance of shot, how clean was shot and accuracy of shooter. I wonder if, in hind site, prevention was the solution, if all precautions where taken: Were the guides expecting  bear in bear country? Looking for sign, making noise and taking the safest trail possible? Maybe. I hope the lady recovers.