In-Universe example: Nigel and Marianne spend one episode trying to film the bird-eating spider. However, Marianne is frustrated at how many of Nigel's turns appear to be false, instead leading them to other prey-species that are apparently dead-ends. However, Nigel points out that the Bird-eating spider rarely eats birds (Which is actually true!) and that by finding the species that the spider primarily dines on, they'll be much more likely to find the spider than if they followed birds.
So Eliza can talk to animals and just generally understand their speech, and her parents film a nature documentary. What happens whenever they film footage of a predator killing and eating it's prey? Imagine what something like, say, the sea-turtle hatching season - in which a LOT of the baby sea turtles get picked off by birds and crabs and other predators before they even reach the sea sounds like to her? Of course she rarely sticks near her parents when they are filming but she must have experienced this sort of thing at some point in the wild just by happen-stance anyway.
Mating season, both in the wild and in nature documentaries, as heard by Eliza. Imagine walking through a forest and suddenly you hear what sounds like a porno, made even more awkward by not being able to tell if it's coming from humans or animals, since animals sound like humans to her.