"I always thought it would be different when I went back, but it was not," Gibson said in the lawsuit. "I stayed as long as I did because of the children and because I needed a job."
Last week, Lowe sued three ex-employees, including Gibson. He claimed she demanded $1.5 million to remain silent about the abuse allegation, which his attorney dismissed as "outrageous" and "untrue." In that lawsuit, filed in Los Angeles Superior Court, Lowe also accused another nanny of spreading lies about him.
Gibson's countersuit, filed Monday, seeks unspecified damages.
Her attorney, Gloria Allred, told The Associated Press that Lowe filed his lawsuit after his attorneys saw "the original content of our suit."
"They may have thought their pre-emptive strike would intimidate our client," Allred said Tuesday. "I can assure them it will not."
Lowe, 44, is a former star of "The West Wing" and now appears on ABC's "Brothers and Sisters."
He gained attention in the 1980s as a member of Hollywood's so-called Brat Pack, appearing in films such as "The Outsiders," ''Class" and "St. Elmo's Fire."