Good nutrition. The best way to get vitamins is in your daily diet. If for some reason your diet is limited, then be sure to get enough vitamins d, c, b's, and calcium and iron. Discuss your diet and nutritional needs with your doctor.
It depends. Teach kids to get their nourishment from fruits, vegetables, milk & occasional lean red meat & the answer will be "none". However, teen girls struggle to get enough iron and calcium through diet alone. If you feel she really isn't getting adequate amounts of essential nutrients, I recommend a basic one-a-day w/ iron & 6 ounces of calcium-supplemented orange juice with breakfast every morning.
Any teen vitamin. There are several brands of multivitamins for teenage girls. They all have similar ingredients. So, any brand labeled for teenage girls should suffice.
A good quality MVI (multivitamin) A good quality MVI that will dissolve and be absorbed is best. A cold pressed vitamin is usally aborbed better than others. They are found in nutrition stores. A growing 15 year old especially needs 5 dairy servings a day or needs additional calcium supplementation (500mg twice a day) that is in addition to the multivitamin. If eating 9 fruits/veggies a day you don't need one!
Standard MVI (multivitamin) The aap recommends universal supplementation with vitamin d for all infants, children, and adolescents. Any standard children's multivitamin that contains 400 iu of vitamin d should be adequate supplementation for your teenager. The vitamin will be better absorbed if taken at mealtime.