If she still has milk and all three babies are ok, and she is happy then i think she should feed as long as she wants. It's important to look after oneself whether one is breastfeeding or not, but i doubt she'd gain weight if she weaned if she really IS anorexic. If she is just very thin then that doesn't mean anything really, you can be very thin or very fat and the milk is the same.

Most women lose their milk to some extent in the 2nd tri and then start making colostrum so her toddler might be getting alot more comfort than he is milk. I'd be inclined to think that closeness with the toddler now, especially with the busyness and demands of twins on the horizon, is precious and should be enjoyed.

One can LOOK anorexic without being anorexic. There was a girl in my school who i later lived with in halls and once calorie counhted with her. Her BMI was 16.5 but i kid you not, she ate 3000+ calories a day. SHe found it SO hard to gain weight, but it was just her metabolism. ANd there again there was another girl whose BMI was 18 and she quite obviously had an eating disorder. SHe was vegetarian, then vegan to cut out food groups she thought were fattening, she walked for 4 hours every day, she used to hollow out her bagels before she ate them (!?) and ate, she once proudly told me when she "caught" me on my 2nd slice of cheesecake (i wasn't hiding from anyone, but i was overweight and complained about it a lot), 600 calories a day.

It's hard to tell just from looking what someone's eating habits might be.

Bx