It is important to note that not everybody has the same body type. Some people aren't meant to be 100 lb. or less. It all depends on your build, your figure, and your bone structure. If you're taller, for instance, you're going to weigh more than someone who is short. If you have a muscular body, that will also weigh more since muscle weighs more than fat.
For example, I am very tall, and I have a wider build, while my friend is short and petite. She has lots of muscle, but overall her figure is tiny. It's easy to compare yourself to people like that and think that you need to be that tiny as well, but don't do that, because, as I said, it's all about body type. You are beautiful, no matter what figure you may have.
Now I know all of this seems rather obvious, but I say all this to show that in the end, a healthy body comes down to far more than just a number on the scale, which is something I often struggled to realise until recently.
There are three overall female body types: the mesomorph, ectomorph, and endomorph. In order to explain more efficiently what each body type entails and which one you are, I have included this very helpful video. I hope it helps!!!