She may serve the full 60 days. Good time is awarded when you're sentenced to more than 1 year.
18 U.S.C. 3624 (b) is the law that addresses federal good time credit. The statute provides for the award of good time credit for satisfactory behavior by a federal prisoner who is serving a term of imprisonment of more than 1 year, but less than life. Those prisoners sentenced to life are ineligible to receive good time credit.