Can a bus company be held accountable for the actions of one of their drivers?

My wife was boarding a crowded bus during peak hours. She was carrying a cat in a carrier. She was standing behind the yellow line and as others were boarding, she put the cat on her shoulder, which is painful since she is disabled. The driver said she had to move. She asked him to get her a seat showing her disabled I.D. He proceeded to call her a "500 pound bitch " 3 times at least. He then incited the passengers by telling them she was delaying the bus." We don't move until this 500 lb. bitch moves. And he didn't. Not one person offered her seat. Then, he allowed a passenger to exit by the rear door, come around to the front and say, "You are a selfish c**t. After more comments a woman from the rear yelled," Let me up there, I'll kill her and the dam cat." Finally a older man, gave up his seat. He went right where my wife was standing, and the driver had no problem. She could not get on another bus, so she left. this was on 3/6 2014