She's obviously smart and understands/wants learning and research. Maybe you could use that to your advantage... teach her examples of human history and current societies that rely on meat and hunting and fishing and how that's helped us/them evolve/survive. Mothers with breastmilk production issues in the past could not always rely on wetnurses, they used cows milk or goats milk...Her views really only apply to a modern society where a vegetarian diet is actually available. Try relying on vegetables in the arctic, now or 200 years ago. She's missing some information; if she really desires to give this speech, she may need more information so that it's not one-sided, geographically-unique or economically biased.
Then again, she's 10, and I don't have a 10 year old, so maybe I'm being too logical and critical of the topic for someone of that age.