I would straight drown that girl. If I even came up and saw something like that its for sure I'd be in jail that evening. I don't understand how people can abuse poor defenceless animals like that. That girl has some serious mental issues.
Drowning her would make you no better than her. IMO it's not right for people to get away with this without a punishment - but the consequences must fit the action. In this case, I'd settle for a combination of prison time and mental health therapy to correct any mental issues that she does have. The question though is where to draw the line, if we assume all life is equal then many people are guilty of killing ants and would get the same punishment as killing a human which for most wouldn't make a lot of sense.
Hey bud, I would not have killed her.. just scared her a bit is all. I can tell you this, animal abuse is an early sign of being psychopathic and I don't know but I doubt there are many drugs or doctors that can fix that issue. Sure they can keep her sedated but that's no fix.. Just lock her up and forget about her.