[help] at what point do I stop being kind and start being cruel?

14+ year old German Shepherd mix. I live in a house with 5 steps in/out. Dog falls 2-3 times a day going in and out of house. Juneau is the wife's dog so she sees it a little different than I do, but I think it's time to put her down. I'm kind of the opinion that I don't want to "have to" put her down in an emergency because she finally got a real injury falling down the stairs. What have any of you done in this situation? I've tried to talk to the wife about this and she is off the "it's fine" opinion. via /r/dogs http://ift.tt/2rFAs0B