I've been vegan for many years and I brought my kids up on a vegan diet. As a pp said, the best advice is to get advice from a dietician if you're unsure about how to do it.
My kids have always eaten lots of beans, pulses, lentils, tofu, tempeh, nuts, fruit and veg, dairy alternatives, fortified foods. There is plenty of vegan junk food too to eat at parties etc. My kids have never been left out but that was probably more to do with having nice people around us. There were other vegan kids and vegetarians too.
I always gave my kids a multi vitamin but I'd have done that even if they weren't vegan.
One of my kids has tried cows milk and eggs for a short time when they were older with no allergic response. He's back to being vegan now.
My kids are healthy. I didn't have any issues in pregnancy, I've never had low iron, but I've always eaten a healthy vegan diet. I breastfed my children until they were over 2.
I think your daughter should get advice from a dietician (not a nutritionist who needs no training) and see how it goes.