Lower Merion Township police say the bank robbery was an inside job.
Police say the woman, 19-year-old Calia Kane, was a bank employee at the Wells Fargo, on the 300 block of Levering Mill Road.
Investigators say she conspired with the armed bandits, who have been identified by police as Malcolm Moore and Marquis Wilson.
The third man seen on surveillance remains on the loose.
"They were very aggressive, they displayed their firearms. They threatened the employees and the customers. Fortunately, there were no injuries and no discharge of the firearm," said Supt. Michael McGrath.
Police say the trio fled to Atlanta where they were arrested with the help of the FBI on Tuesday.
They will be extradited back to Pennsylvania.
A separate investigation is still underway into whether the suspects were involved in a near-identical robbery in East Pikeland, Chester County, days later.