The actual sentence was 30 days but it was halved by day-for-day credit.
Blumenshine already served four of the remaining 15 days before she was released on bond.
After her arrest, Blumenshine was subjected to a sex offender evaluation.
In addition to the time in jail, Blumenshine, 30, was put on sex offender probation for two years and will be placed on the Illinois sex offender registry for 10 years.
Blumenshine faced much harsher penalties but prosecutors dropped a charge of aggravated criminal sexual abuse and replaced it with a charge of traveling to meet a minor, a class three felony.
"I have been holding down a ' Teller Position' at the Marseilles Bank for the last year," she wrote in the letter.
Blumenshine and the boy had texted each other to set up the rendezvous, said Assistant State's Attorney Frank Byers.
Plainfield police officers reportedly noticed two cars parked alone together in the Kohl's lot, and when they went to investigate, found Blumenshine and the teen in one of the vehicles.