(PS We do not "Know" she assaulted anyone. We only know there is an allegation she did so. But we do know he popped an old woman with a Tazer, that was sitting on a bench. I don't think it can be justified to taze someone because of an allegation. You can only justify it if the person is a threat, in my opinion)
We do know, she plead no contest to domestic assault (of her grand-daughter no less)
You did make a correct statement in that you cannot taze someone because of an allegation. She was not tazed because of an allegation, she was told she was under arrest because of an allegation. You can arrest someone for that. Then they go to trial. She was tazed because she was resisting arrest. Once again, here are the options in this case:
1. use physical force to affect the arrest (grab, hold, even up to strikes)
2. pepper spray
3. taser
4. baton
5. firearm
Which of these presents the least probability of the officer and the subject being injured? (let's take out 4 and 5 for the sake of sanity).
option 1- the officer might possibly be hurt (unlikely). the granny might be hurt (possible)
option 2- the officer might be hurt (enclosed area increases chance of officer and any others being contaminated by his own spray). granny might be hurt (maybe, due to the fact that she still must be forced to the ground after being sprayed)
option 3- officer is not in any real danger. granny has a .00162% chance of being killed by the taser and also a chance of injury caused by the fall.