Lord, people are stupid. It's a wax tablet. Ancient Greeks and Romans used them for temporary writings that weren't worth committing to parchment. Its presence on a tomb sculpture indicates the woman was literate. The attendant is bring her mistress a written message to read, perhaps from an absent husband, or perhaps a draft of a poem or something. The conspiracy theorists try to argue it can't be that because it's too thin (it isn't), because she's looking at the top tablet like a laptop screen (people would write on all surfaces of the tablet), and because she doesn't have a stylus (she's reading, not writing).
But what about the "USB ports?" USB ports are rectangular, not circular. If the artist was paying enough attention to detail for the thickness of the object to matter, surely they would have gotten that detail correct. Actually, there's a very obvious reason for those two holes.
The slab of limestone wasn't thick enough at that point to get the complete depth needed for the attendant's hand holding the tablet. So the sculptor drilled two holes and used pegs to attach the rest of the hand (now lost). Alternatively, it may be a repair if the original carving of the hand broke off. But they are quite clearly peg holes.
The real interest of a piece like this is that it is evidence of the prestige associated with women's literacy, which is important since we have so few surviving writings from female authors in this period.