This quiet, but friendly little girl is a six year old thilashin. Thilashins, or "possessors of morality," are often mistakenly referred to as nuns. Practically speaking, if you ask me who she is, I'd probably say she's a nun because that's much more relatable than a word that is Burmese.
Thilashins fit in somewhere between an ordinary Buddhist follower and a proper Buddhist nun. In modern Burmese Buddhism, women can not attain an ordained position, similar to that of a nun. Thilashins also follow the Ten Precepts, which is a basic code of ethics. I'm probably not getting it 100% right, as I'm not Buddhist, but that seems to be the gist of it.