Track you and your childrens food intake for a few days, diferent days, different week. The numbers will prove that EDUCATED vegan/vegetarianism is the most healthy liestyle.
You are a mindful parent, and this is teaching your kid a whole lot of lessons: eating healthy, communicating, debating, being different, caring about more than just humans. I hope your daughter learns strength from this, I have a lot of respect for that girl
Unfortunately, teenagers who turn to vegetarianism often live off potato chips, from what I saw. I wasn't, I must bhave gained 40 lbs in one year around grade 9 from stress, eating, sadness

It's hard to be a kid. Sometimes I wished someone had said something in a.. smart way.