Stefany had asked the judge last month to quash the subpoena from Brown, saying her testimony would not be relevant in Brown's criminal case.
Brown has been charged with defrauding Agora and three other charter schools she founded and then participating in a scheme with two other former administrators to cover it up.
In her filing, which she wrote, Stefany asked the court to "consider the possibility" that she was being "subpoenaed to testify for the defense in this criminal proceeding as a further attempt by June Brown . . . to intimidate and defame Mrs. Stefany."
After jurors in Brown's case left the courtroom Thursday, Brown's attorneys told Surrick they believed Stefany could testify that the for-profit K12 Inc. of Herndon, Va., had used her and other parents to force Brown's Cynwyd Group out of a lucrative contract to manage Agora.
Federal prosecutors said Stefany's testimony would be irrelevant because Cynwyd's management contract with Agora was fabricated.
Brown cut her ties with Agora in 2009 as part of an agreement settling several lawsuits, including one involving the state Department of Education.
Brown sued Stefany and five other Agora parents who had raised questions about the school's finances and its relationship with Cynwyd. Brown's firm owned Agora's building in Devon and collected management fees from the school.
The slander suit Brown filed in Montgomery County alleges the parents had made comments "that give the clear but false impression that Dr. Brown is corrupt, incompetent, and possibly criminal."
The defamation case is on hold, pending the outcome of Brown's fraud trial.