If you monitor her weight and she's losing weight quickly instead of mostly staying steady, that's when there would be a problem. I know somebody on here has numbers on when exactly you should start getting worried (a % weight loss over so much time) but I'm not sure I remember it, so I won't say. If she'd dropped 40 grams in one month, then 40 the next, then 40 the one after that that would definitely be a problem.