Health experts! ANOREXIA question! 16 yr old?

if someone becomes anorexic and loses about 50 pounds and then she gets better will she gain all the weight back? what if she goes to a nutritionist and increase her metabolism rate by exercising and eating healthily will she gain all the weight back? if someone's metabolism rate is high and eats healthily she wont gain the weight, right? if she becomes healthy after being anorexic will she gain all the weight? would she be able to maintain the weight?