I’m pretty sure this is either a Commodore or a Rear Admiral Lower Half. All admirals in TNG had pips framed by a box. They just likely changed the look to be framed by a trapezoidal design.
I’m intrigued by the potential notion that this might be a Romulan officer in Starfleet. At first, I’m wondering why she would have a differently-designed rank device, if it is a specifically Romulan designation. Then I remembered that the Maquis officers in Voyager all had different rank devices, as “provisional” non-Starfleet field promotions, all basically having a Starfleet analog of equal standing (but not quite).
If there is some joint Romulan/Starfleet officer exchange going on in the 25th century like they had with the Klingons in the 24th, it would make sense that there would be a subtle indication as to the officer’s origins. Also similar to T’pol’s maintaining of the Vulcan “Subcommander” grade on Archer’s Enterprise.
I definitely feel like some story elements in this new show have been potentially lifted from STO. Not sure if this is a good or bad thing yet, if true. We shall see.
I am very pleased that they got rid of the silly bumpy-headed Romulans in favor of more TOS-looking ones. Never liked the bumps for them. It seemed particularly silly to me that Spock could walk freely amongst them (ostensibly, in disguise) in “Reunification”, when none of the TNG Romulans were smooth-craniumed. He should have been immediately outed as a Vulcan, especially since they went out of their way to give both Picard and Data head bumps to “blend in”. Really bad sub-plot hole there.