Karen Plankton was a computer that lived in The Chum Bucket in Bikini Bottom with her abusive husband, Plankton.
Nothing is known about Karen's life before or as the outbreak began. She may have been abused by Plankton but this was not explored in this show.
When the power started to go out due to Power Plant workers being devoured by zombies, Karen automatically died due to loss of power over a period of time. There is still a chance to bring her back to life if the apocalypse ever ended and true power was restored but until then, she is dead.
This list shows the victims Karen has killed: