The only thing you should worry about if youre vegan is B12, which you can easily get in fortified plant milk, cereals, some breads and as supplements. Otherwise, just plan what youre gonna eat, make sure you have a source of plant protein, and if youre worried about gaining weight, which happened to me when i started out, just eat more green veggies, lots of spinach for iron also. Your mom has nothing to worry about. Im 16 and ive never felt better on a vegan diet, just make sure you get all the nutrients you need! Also if you stick to wholefoods its much easier to be healthy. Enjoy 🙂