We mostly do not see it this way with an animal who suffers. Euthanasia is completely accepted when we know the animal only feels pain and misery and their is no cure. I think most people do not see this as harming.
You can also reason that when one does not euthanize, and someone suffers very much in a way of anger, extreme agitation, an impossibilty to be not agitated, in panic, with strong longing for the end, one harms that person.
Maybe because of all this anxiety someone will be born in a bad state. With euthanasia one can die in a peaceful manner. When even such a person as Channa cannot bear severe pain and misery than how much worse will this be for a worldling?
Another way of dealing with extreme suffering is to use so much morphine that someone enters a kind of coma. And by not eating and drinking one will die after several days. I also heard of people who stopped eating and drinking on their own initiative and left.
I think harming is questionable view on euthanasia.