[HandyDandy]

I concur with the author of the article.
”What was once thought to be a somewhat glum depiction of a young girl reading near a window is now an amorous portrayal thanks to the unveiling of a naked Cupid hanging in the background.”

[Tax-chick]

The young woman’s expression and posture didn’t change. If she was “glum” about unknown contents of the letter, now she’s “glum” about whatever romance is conveyed by a giant, naked baby. And well she might be, considering childbirth in that era.

Maybe Vermeer’s original patron asked for the picture on the while, while a later owner said, “Meh.”