A) If she can't explain why, then she's retardedly following an ideal she doesn't actually understand.
B) I hope I don't offend by the stereotype but she's a girl, last I checked most aren't concerned with gaining substantial muscle...
C) How can you pump up a balloon if you periodically deflate it afterwards? Answer: Not at all, or very slowly.
D) What do you do when you're trying to gain muscle and its just not working even though you're getting proper recovery time? Eat more. Eat more. Eat more. Its the easiest solution to get past these plateaus, so its really hard to maintain the SUPER clean bulk.
E) Try to have a normal life, GAIN muscle, and stay at very low body fat. Try it. The dedication one needs to accomplish this isn't worth the effort unless having such a body pays for itself. I'm not even going to fragment it in words, it needs to be experienced what a nuisance this can become balancing with your job, going out to eat, performing well in sports, etc.
Although I will say I know what she's talking about. If you increase the frequency of exercise while improving your diet you're bound to add muscle and lose fat at the same time. So in a sense that people constantly polish their exercises / diet, theoretically they'll improve their muscle gains while losing fat. But again, this relates to the person's dedication and other constraints in their lives, so improvements will become less and less substantial until this plateaus.
Thing is, after so much experimentation, I found what most others here preached before me.. It's so much easier to gain muscle with a little bit of chub that you could lose in 1-3 weeks if you wanted to. Then, you just keep it in control with periodic cardio.
When you exercise beyond how much you eat, or without enough recovery time you never really experience your size gains. Sure your shape will change because of atrophy but since the muscles never really recover in time to notice appreciable size gains, what's the point? If you have an energy surplus (a little healthy chub) and fully recovered muscles you're ahead of 99% of the population, seemingly. This combined with the know-how you could easily cut the chub off for your next beach outing really sold me. Gain in the winter, cut a bit in the summer.
I suppose Strength + body weight age better than dexterity & reflexes so its kind of silly to stay small as you get older being a guy 20+, unless you're worried about heart problems, etc.
Though, for the men: If you're looking to hook up with younger girls, by all means stay skinny..
14-17 year olds will hit on me when I'm skinny, but with a little bit of chub and the easier to sustain muscle gains that go along with it, I'm in my own age range. Its weird. Oh, and happy birthday to me.