Sarah Walker (mirror)

Sarah Walker, more commonly known as Anna Walker, was a Terran Starfleet officer in the early 25th century, and commander of the as well as Starbase 144. 

Assimilation and Separation
Little is known of the circumstances around the incident, but a mirror counterpart of 11 of 14 has bee stated to exist.

2410
Anna Walker somehow reached the rank of Fleet Admiral and became commander of the.

Mirror Alliance Opposition
When the mirror universe Nat Wallace worked alongside the alternate universe Nat Wallace, apparent AU Sarah Walker, and the prime universe Captain Krystal Jade, Mirror Nat proposed having AU Sarah take place of Anna to give the Alliance additional power, and had run several simulations to prepare for such a plan, but the plans were eventually scrapped. 

USS Sally Subspace Invasion
When the USS Sally (NCC-201591-F) was lost in subspace and boarded by numerous enemy factions, Anna Walker eventually intercepted and boarded the vessel in an attempt to kidnap Krystal Jade, but failed and eventually retreated, but managed to steal the in the process.

Temporal Fracture Outpost Infiltration
When aliens began fusing alternate realities together from a secret base in a temporal fracture, Anna Walker eventually arrived in a scheme to get vengeance against Krystal for her previous failure, but eventually decided to assist them in their mission instead.

Alternate Universes
There are, as of 2410, 2 alternate universe versions of Sarah alive; including Admiral Sarah Walker from the alternate universe accessed via a wormhole in the Natara Expanse of the prime universe, and her prime universe counterpart.