I would start helping her make that connection between animals and foood, not being too pushy (
Best not to go in too hard reminding them about roasts while they are patting the baby lambies though
) but not denying it if the question comes up.

I imagine it would be easier to accept at a younger age, and grow up accepting it, than to realise one day when she is 5 or 6 while she is at school or watching play school or eating a lamb chop (got the Simpsons episode of Lisa becoming a vegetarian in my mind).