Your neighbor is correct. She would also be correct if she said elder was very toxic to humans…assuming the human was eating very large amounts of it because the human identified as a furry herbivore.
As a medicinal plant in medicinal doses, it’s perfectly safe for goats (or humans that think they’re goats). As a forage, eaten in large quantities, it’s potentially toxic.
Don't use herbs or combine herbs with medications or use them during lactation or pregnancy without talking with your healthcare provider.