Appearances of Matrix
Matrix, the Pocket Universe Supergirl, first appeared in Superman (DC, 1987 series) #16 (April 1988). She was brought back to the primary universe in Superman (DC, 1987 series) #22 (October 1988). Matrix merged with Linda Danvers to form a new Supergirl in Supergirl (DC, 1996 series) #1 (September 1996). She was separated from Linda in issue #50 (November 2000). Matrix merged with Twilight in issue #74 (November 2002).
See also [Supergirl [Matrix & Linda Danvers]][16210] and [Supergirl [Linda Danvers]][29394].
[16210]: https://www.comics.org/character/16210/
[29394]: https://www.comics.org/character/29394/