I guess our point of disagreement is where the line is. If her deficit was a little higher (corresponding to lossing 2+ pounds a week), I agree with everything you said. I agree calorie deficits inevitably lead to muscle loss in men and women. I agree testoterone is helpful for maintaining or building muscle. I just don't think a 900 calorie deficit for four months will result in a grotesque loss of muscle (or a "dangerously high body fat percentage"), especially given her muscle building exercises. Losing the weight slower (like a 500 calorie deficit/lose 1 pound a week) will result in less muscle loss than her current strategy. We agree on that. Curious: where would you draw the line? Btw, I bet 25-30 pounds difference on a 5'4 woman is most of the difference between a healthy bmi and being obese, so let's not minimize the health benefits of losing the last 25 pounds.