Technically, fasting doesn't help you lose weight. Fasting slows your metabolic rate down so your diet from before the fast is even more fattening after you fast. Also, you are not getting proper nutrition which can lead to fatigue. A better alternative is to eat vegetables to help you feel full, drink plenty of water, get tempting foods out of your home, stay busy because you don't want to eat just because you're bored, don't skip meals, and EXERCISE!
Talk to her privately, she may be going through a tough time at the moment, ask her why she thinks she believes she needs to loose weight. If she does need to lose weight, due to this person having a higher weight scale. ( If she is over weight only! ) Tell her fasting is not the best of an idea, ask her to go for a walk, go to the gym, say something like '' Yeah! I've been meaning to go myself, I'd love you have you accompany me! '' .
