Plants don't have:
Vitamin A, B6 (Pyridoxal, Pyridoxamine), B12, D, E (Animal) F, K2, Q10. Amino acids: Creatine, Carnitine, Carnosine, and Taurine. Heme-iron, Collagen, CLA (Omega 3), Cholesterol and Complete Protein (Consists of 9 essential amino acids)
Antinutrients & harmful substances in plants: Alkaloids, Alpha-amylases, Arsenics, Cellulose, Cyanogenic glycosides, Fiber, Flavonoids, Gluten, Lectins, Mycotoxins, Oxalates, Phenolics, Photosensitizers, Phytic acid, Salicylates, Saponins, Sulforaphane, Tannins, Terpenoids and etc.
A vegan diet indeed prevents heart diseases, by delivering you to the grave long before the coronary risk comes.
OP: As a teenage girl, you are going to struggle hard enough with body changes without undermining your health with this contrived "plant-biased" nonsense, especially when it comes to the iron and B12 anemias, which are devastating to a runner's career (I had them even as a young man veggie). And despite what the V-people would have you believe, taking pills does not compensate for natural, bioavailable forms of nutrients found in meat, fish eggs and dairy fat.