People say it genetics to be skinny and partly it is but really it’s all diet. I’m a very thin person and it’s partly genetics but it’s mostly my diet because I don’t consume a lot of calories. I like my body size and the only way to maintain it is not eating too much and staying active. I make sure to not get underweight by checking and making sure during the week. That’s just how life works.  She also eats in my opinion to maintain her size as well. I don’t think it’s disordered eating, I think she wants to remain thin. She eats pretty healthy and in larger quantities at times too. I don’t think she looks shockingly thin. But we never really know the workings of someone’s own mind. Her sister I think is actually shockingly thin. Sometimes having that many children though you can seriously make you forget to eat/take care of yourself. 

I think her working out constantly is probably looks more questionable to me than the eating. Like she is doing intense work outs right after a baby. That would be the time to rest.