sorry 2 be controversial but i think telling her in a gentle way is a better alternative. my mother is a vet nurse and she never hid the fact that, in the wild animals don't always live long lives. it has not hurt any of her kids knowing this and i feel is beneficial to all involved, you don't have to lie and your daughter is taught about this by you rather than others that may not know how to talk about it with her in a calm and considerate fashion.