"The girl is wearing a jewel."
Translation:Το κορίτσι φοράει ένα κόσμημα.
It could be, but the problem is, these two words are not always interchangeable. In fact, the cases that these two words are indeed interchangeable are really few, almost idiomatic. Στολίδι is more commonly used to describe an ornament, some sort of decoration. You hardly ever hear it for jewelry ( you might come across it in poetic speech or literature. Even so, it's still uncommon).
So in this case, I think we should keep the translations accurate, just to avoid a bit of potential confusion. Thank you for your comment though. ^.^
It can be in some contexts but not in this one.
The hints are global, not per-sentence except to the extent that the system tries to put a relevant hint at the top -- so the top-most one is the most likely to be applicable to the current sentence. Other ones may or may not apply to the current sentence. But even the top-most one may not be correct as the system can become confused e.g. if there are multiple similar words in a sentence. (For example, in "I see the man and the woman", it will show the same hint for "the" at the top twice even though in Greek you will need two separate words as άντρας and γυναίκα are different genders.)
Yes, it probably became confused here because το is a part of a correct translation for this sentence -- just not as a translation of the "a" in that sentence!
So the hints always have to be handled with care, unfortunately -- they're not quite clever enough to be as "reliable" as a learner might want.