The York News-Times says Stacy Findley made her plea Monday in York County District Court.
Findley had been working at Petro Fuel Island in York. In February, a manager at the station showed police a security video.
The manager says the video showed Findley doing a return and refund, but no customer was present.
A court affidavit says Findley admitted to taking more than $1,400 in her refund scheme, which she says she started on Jan. 5.
Felony theft carries a maximum prison term of 20 years.
Her trial has been scheduled for July 19.