She had no idea where her child was.
Is Michelle Gregg a bad parent? No, I don't think so. This doesn't mean she's the best parent. I suspect she does an adequate job. Is she responsible for the death of this gorilla? Absolutely. Accidents like this don't just happen. There is always human error involved. Because of her lax judgement an animal on the endangered species list had to be destroyed, and that's a terrible price for not paying attention.