Could have, would have, should have.
She had several kids to look after and to be honest its a bit "Captain Hindsight," of us to point out all the things she magically SHOULD have done. Ideally the Zoo's Gorilla pen shouldn't be so easy to get into that they depend on parents watching every single second of their kids and keeping them on a leash just to prevent them from falling in.
Her kid asked a ridiculous question, the sort of dumb questions kids always ask and parents say no to. Yes, if only she was psychic and took THIS specific request seriously, OH IF ONLY!
Thanks Captain Hindsight.