How about 90 days in jail, then required psychatric treatment and a bar working with animals or small children. Mental illness can cause people to do horrible things, but she was clearly aware of her own problems, and should have avoided such situations were she could be dangerous. That's some jail time for putting others at risk when you have a known problem. Other than that, she obviously needs help and since she can't keep herself away from animals, the law is going to have to do it for her.
Since I don't know enough of the details, I can't say much about her defense attorney . . .she may be authentically crazy and did not mean to do it . . . but then she should be punished for working with animals while knowing herself to be mentally unstable in a way that could cause her to hurt the animal.
From what I know of such issues in the law and criminology . . .which isn't much, because I don't do criminal law, but from what I know, despire popular belief, people do not simply snap. Oh, sure, they may in the sense of finally throwing a punch at someone, but acts of real, serious violence, like this, are always proceeded by plenty of warning signs. She didn't just smack that dog, she tortured it. So I doubt this is the first time her mental ilness resulted in aggressive behavior . . .the minute she, or her fiance, realized that was a possible outcome, she should have gotten out of the business . . .