Yes, but what is too thin? Is Zacharova too thin? For me not, she is a perfect ballet dancer.
I don't remember the American girl's name who learn ballet in Bolshoi, he was a little bit fat, when she arrived in Moscow. Now she completed her studies, I saw a video she became more thinner.
But don't get me wrong, I think Mao, Caro, Yuna and many others have good body types, I like them.
I believe the American girl is Joy Womack (been watching ballet now for the past few years).
Her body type may not be considered ideal esp. in Russian ballet, where little girls are examined head to toe for an "ideal" body type before a group of stern discerning women who will in no uncertain terms call one girl or another "too fat", "stumpy-legged", "big head", and so on... Look for a video called 52 percent, which is considered an ideal leg-lower torso ratio to the upper body.
As for Svetlana, she has a body and balletic qualities to die for, but her foot arch may be considered a bit extreme, and she is known more for her ungodly extensions, supple spine and lines more than, let's say, quick strong footwork (petite allegro for example) Some shorter, less "ideal body-type" ballerinas may be much stronger for fast footwork and turning pirouettes, and their fouettes may actually look nicer because their legs don't hyperextend as much. A very strong dancer in the 60's was Eckaterina Maximova, who danced with her husband Vladimir Vasiliev. Not ideal Russian ballerina body for today- today they are looking for a tall slender Sylvie Guillem body type- but perfectly acceptable back then.