In 2374, Doctor Loews was posted to a Federation Institute where she was responsible for the care of a number of patients who had undergone a procedure called accelerated critical neural pathway formation. This procedure had left Loews' patients with extremely advanced mental abilities, but severe problems integrating with normal society.
After the revelation that Doctor Julian Bashir had also undergone the procedure but had managed to maintain a normal life, Loews took four of her patients – Jack, Lauren, Patrick, and Sarina Douglas – to Deep Space 9 in the hopes that Bashir could show them that it was possible to function in normal society. (DS9: "Statistical Probabilities")
Karen Loews was played by actress Jeannetta Arnette.
The spelling of Loews' name comes from the script for "Statistical Probabilities", which also gives the pronunciation as "LOWS", going on to describe her as, "...a Starfleet psychiatrist of about thirty-five. Though by nature a warm person, she's been working with Jack and the others for months now and it's been a difficult time." This would suggest Loews was born around the year 2339. 
In the Star Trek Online novel The Needs of the Many, Doctor Loews' work with the patients at the Institute makes a contribution to helping the rehabilitation of genetic augments. Among these is Jack, whom Doctor Loews certifies of being free of any side effects of his childhood genetic alterations.