What is the best way for a teen to get her period back after excessive dieting for 7 mos?

Better diet: Your body needs enough good cholesterol and fats so that your ovaries can make the hormones (estrogen and progesterone) you need to have a regular period. Excessive exercise can also keep you from getting your period as it shuts down the ovaries.

Gain weight: I would advise getting a checkup, to make sure everything is alright. Unless and until a female attains a minimum amount of body fat, menses will not resume. See a gynecologist who can best address this matter. Good luck.