A good healthy weight for an adult female is between 113 lbs to 138 lbs.
Some woman are a little less than 113 lbs in weight and it can be okay but if you're under 100 lbs and are 18 or above then that can be unhealthy.
But it also depends on your height.
I'm 5 ft 8 inches so almost 6 ft tall and I weigh 130 lbs.
My sister is the same height and weighs 110 lbs and her doctor said she's healthy and nothing is wrong with her and she eats quite a bit of calories.
She just can't seem to gain any more weight than she already has.
She eats really good but no matter how much she eats it seems her body doesn't want to make any fat.