Just tell her the most likely truth, the only thing that is observable.
There likely isn't a god, but many people believe in different things. All we know is that when people and animals die, their bodies are turned into compost by bugs, bacteria and worms, and that compost creates new life, by making plants which feed animals (including humans). And so the cycle continues.
It is beautifully simple and all completely true.
Your child will find their own way when they are old enough, if or when they decide to believe in non fact based explanations. why burden them whilst so young, they accept reality without question and it is not scary to them?