
Is this a folding mirror case like extant ones? The date matches the artifact. The lady appears to be adjusting her hair or checking her face suggesting mirror. It's in 2 pieces, but she only needs to hold one, so it's joined. Perhaps another comment on the vanity of women? I had wondered why there weren't pictures of hinged mirrors since there are quite a few extant ones in the very early 14th century and written about in the 13th century, so maybe, yes there are, and we're looking at it right now.
She isn't accompanied by musicians so I feel she's not an entertainer.
Here's what an extant 14th century mirror case from my collection looks like from the non-mirror side:

A few people suggested glasses, and while glasses do turn up in written records earlier than we see them shown in art, this would be the earliest depiction of them, and I do feel that her pose is more suggestive of attending to a stray hair or her face.

David being anointed. Bute Master (Franco-Flemish, active about 1260-1290)- Initial D- The Anointing of David. Google Art Project.