That being poor is not a get out of jail free card for painfully drowning animals.
Yeah, I didn't mean to imply that poor people have a "free pass" so much as that poor farmers are going to very often be in a situation where:
a) They've got unwanted/sick/dying animals on their hands.
b) There is no authority that will assist the animal.
All of that adds up to the animal getting thrown into a body of water.
I think I understood that you weren't condemning the girl, but my point is that you probably shouldn't condemn the adults either. Those puppies getting thrown in the water is just how it's done in those situations.
While I also understand your point, that there are potentially more humane ways of doing it, I think it's pretty unrealistic to expect people to pursue those, and thus it's unfair to condemn them for not doing so.
Also, even if the people elect not to, say, decapitate the puppies, they'd be doing so out of an excess of empathy for the puppy, rather than a deficit. A cruel person would probably enjoy the "up close and personal" killing more, because they'd be involved. A "normal" person responds by trying to distance themselves from the killing, both my joking about it and by using a mechanism that is physically distant.
In short, this is normal human behavior, and really, normal llife on a farm.