The counterpart of Beckett Mariner from another quantum reality, a stern captain of that universe's USS Cerritos who uses the name Becky Freeman, seen in the Lower Decks episode Dos Cerritos.
Captain Becky Freeman is an alternate version of Beckett Mariner who appears in Dos Cerritos, the first episode of the fifth season of Lower Decks. The Cerritos is pulled through a rift into a parallel reality and meets its double, a ship run with harsh discipline by a Mariner who took her mother's surname and rose to command. In that reality Carol Freeman has been transferred to Starbase 80.
The two crews compare notes. The other Rutherford has embraced his implants completely, and that universe's Boimler is a more assured officer than the one visiting. Becky, tired of the weight of command, envies the easier life of her counterpart and traps the prime Mariner so that she can take her place.
Mariner gets free, tells the other crew that she is not their captain, and the ships part. The meeting leaves Mariner glad of who she has become, and the rifts go on to drive the rest of the season.