It's mildly justified. If the lady did not open fire, the police probably would not have returned it. However, if you're in that situation as an officer, you bust down a door and end up being greeted with gunfire, you will fire back. I don't think anyone would
not fire back. A 92-year old with a gun is not necessarily different than a 20 or 30 year old with one. However due to her age, yes, it probably was confusing and difficult for her to tell what was going on or who was entering her house, perhaps why she decided to fire the gun in the first place.
Have a look at
this, too - These are incidents which are unjustified. If the woman was indeed selling drugs and there was a warrant for her arrest or the search of her house then the officers were in the right and acted accordingly.