Stephanie Merlo is charged with institutional sexual assault and corruption of minors.
Investigators say Merlo met the alleged 17-year-old female victim while coaching at Pius the Tenth High School in Bangor.
Police say the two had a sexual relationship from September to November.
They also say Merlo provided marijuana to the teenager.
A spokesperson from the Diocese of Allentown says Merlo passed all background checks and clearances.