I would expalin to the lady what I was about to do (not in detail), and try to get her to understand that it would be the best thing for the already injured animal and then take care of it as efficiently as possible with whatever possible. If for some ungodly reason the lady objected to what I was about to do--to dam bad--I'll have self apponted operational command of the scene as far as saving any animal from further misery--until someone with a badge shows up to also do that very thing

My Dad and I were traveling a back road coming back from building a tree stand on our property and a small deer (obviously hit) was struggling bad in the middle of the road. The car that hit him must have just driven away (no where to be seen). I pulled overand had to finish him with a 4lb hammer I was using earlier to drive spikes in a tree (had nothing else). A couple cars passed with the people craning their necks--Hey, I had to do it. I'm sure most would have understood.