I am sad that I didn't drive my mother to the airport
Why? Was it because you didn't take those last few moments to spend time with her? Sometimes we have so much going on, we don't have time to do it all!
I had an emergency at work. I am a doctor and it was a life and death situation :( but now I regret because I could have assigned someone else and driven my mother because that was her life visit 
Oh, no, I'm sorry to hear that. You had no idea that would be the last visit, but I can understand how you would feel that way. I have no doubt she understood why you didn't though.