She figured out the process entirely on her own, with a bit of Socratic questioning from me. It went something like this:
N: "How can I fossilize tree sap?"
B: "It would take a very, very long time--millions of years."
N: "If I catch that bug and soak it in agave nectar it will look like amber."
B: "Will it be solid or liquid?"
N: "Liquid...but if I freeze it, it will turn solid!"