Lyn was small (1,58 m), but no less deadly, and sported a droid arm. Although she looked like a young woman, she was already thousands of years old when she came to the attention of the Emperor, who either hired or commanded her services some time after the destruction of the first Death Star.
It is said that she became the right hand woman of Darth Vader, who wanted her to eliminate the leaders of the Rebel Alliance and capture Luke Skywalker - a task at which she did not succeed. She was also among the chosen few that were granted the status of an Emperor's Hand, one of Palpatine's personal elite assassins that were answerable only to him. Nevertheless, she became a traitor, letting Grand Admiral Zaarin enlist her to kidnap the Emperor as part of an attempted coup. Zaarin's plans were thwarted by Thrawn (who was then elevated to Grand Admiral to replace him). It is now known what became of Arden Lyn after that.
To
my knowledge, she doesn't appear in any of the official novels or comics,
only in the Masters of Teräs Käsi game and in fanfiction.