Nobody seems to want to think past first-order consequences: Deputy Donuthole, Granny, most posters on this thread.
And the officer determines the relative health of a suspect... how? If you put that standard in place, watch all the young but frail people getting subdued then suing.
By using his head as something other than a hat rack?
Maybe, just maybe, Deputy Donuthole could use:
Judgment
Discernment
Experience
An eye to unintended consequences
A sense of scale and relative danger to the community
to aid him in his job, rather than the Cartmanesque display on the tape.
My argument is very simple. In some, very limited instances, if a person is so old or otherwise frail that they could be seriously hurt by even a moderate application nonlethal force, the risk to their lives in tasing them is so high that it is better to let them "get away" with something as minor as this than to risk killing them outright. Nowhere did I say that anybody that resists arrest nonviolently should be let go. (Although down here we just grab them by their legs and arms and drag them towards the police car).
This^^^.
Granny poses no risk(1) to the public by driving away from this. Just because one has authority to do some things does not mean it is wise to do some things.
The change I would make to MB's post is that I would take note of granny's ID data: DL#, car tag#, Name, Home Addy, etc. Something Deputy Donuthole already had access to.
Using that data, get a warrant for her arrest. And execute it, say...at her home. Or, better yet,
call her and ask her to come in to get booked and bring a lawyer if she likes. Yeah, she's old and frail, but she earned her ticket and her arrest. All things in good time.
Granny will still end up booked, but the likelihood of her or Deputy Donuthole getting killed by a passing auto or granny dying because the taser is too much for her system have been eliminated. See, Granny is a citizen and taxpayer and her well-being ought to count for something, at least some fraction of the value of Deputy Donuthole's life and ego.
Add to that, there then exists no tape of granny getting tased to get folk all riled up and pissed off at Deputy Donuthole, the Travis County Sheriff's Dept, and LEOs in general.
(1) If she were a risk to others, use whatever means necessary to get her under control.