Not sure how you can 125 and 5ft 6 and have much fat. Pretty much impossible.Some cellulite maybe. Maybe you need to properly test your bodyfat. Remembering that women are supposed to carry more than men they have higher essential fat.
But as said its your body and realize you are not fasting for weight reasons but for better health and mainly saying since you are pretty light wouldn't be doing long fasts but again its up to you.