M.L.
She could need more of the animal fats which are NOT unhealthy especially in one growing. Or low in B vitamins which are in meat. I have read a few times that it is very hard to get all the nutrients you need in a vegetarian/vegan diet. Its doable but it requires things like soaking your grains to sprout them (adds nutrients) and being more deliberate about what you eat. I would read up on it and also consult your pediatrician. It could be dietary - it could be something else and the timing is a coincidence. Does she take fish oil or eat fish? We eat fish often and get it frozen at Trader Joe's quite inexpensively.