I looked it up, she was a Lieutenant commander and his XO on the USS Verity.
A lot of people in Starfleet get promoted to Captain just because they put in their time, but they don't have the chutzpah to command a ship or a starbase.
Or they specialise in a particular area like Cornwell in Discovery.
In Star Trek I have always seen it roughly like this.
Commander in Chief Starfleet
Sector Admirals - 4 pips - Stationary but posted very distant from earth
Fleet Admirals - 3 pips - Mobile with the fleet, many ship with many Captains
Vice Admirals - 2 pips - Highest a medical can go such as Cornwell, very mobile checking on health
Rear Admirals - 1 pip - Highest a non combatant Admiral can go - bureaucrat - stationary - someone like Clancy
Commodore - Special rank for Installations, starbases or security
Fleet Captains - Unofficial if no suitable Admiral is present or required
Captain
Commander
Lt Commander
I would have thought an Odyssey class ship like the Verity would have its own Captain and full Commander, perhaps there was still a shortage of ranked officers after losing so many during the Dominion war.