There is more to this story than we are seeing.
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Well yes. I read the OP and the owner loved the dog very much so she ignored it’s previous vicious behavior (including biting her grandson’s face) because everyone kept telling her not to believe the (documented) stories about pitt bull fatalities and she was fatally more loyal to it than it was to her.
If that is the case, she needed to put the dog down. It’s very hard to do this. I just put my own dog down today because of sickness and old age. Part of me inside died with her aND I hope I see her again in a better world.