Rachel Federickson replaced one eating condition for another. She replaced over eating and general bad health habits with what absolutely appears to be anorexia, bulimia, or a crippling dependence on weight loss pills. There is a healthy balance between too heavy and too thin. Frederickson jumped from one of those regions directly to the other. Instead of being an iconic example of weight loss as portrayed by the media, she has instead warped into the poster child for eating disorders and that thin can indeed be too thin.
Rachel Frederickson finished off the Biggest Loser weighting a measly 105 pounds with a 5'4" height. This puts her BMI at 18.0 which is underweight, but just slightly in real terms. I think it is likely that she will probably gain the needed weight back quite quickly now that the program is over. Typically people do gain weight back after such an experience. The difference between her being underweight and being normal is very small, only a few actual pounds. This, to me, shouldn't stir up a lot of controversy.
If you look at Rachel before and after, it is a drastic change. Rachel needs to find a happy and healthy weight for her that she can maintain. She is a little on the thin side, but she is much healthier. As the excitement wears off, she will gain a little weight back, and be exactly where she needs to be.
No, the Biggest Loser winner Rachel Frederickson did not lose too much weight, because she is still alive and healthy. There were no negative health consequences to her dramatic weight loss. People who are too critical are probably a bit jealous of her fabulous success. She lost the weight naturally.