The 24-year-old had to attend a meet-and-greet session with the students of Barrington High School in Illinois and thank them for raising US$40,000 for Joplin town, Missouri, which was flattened by a tornado in May last year.
However, bad traffic delayed the singer's arrival. "After she was late for more than three hours, we wondered if the event would actually happen," thesun.co.uk quoted local official Jeff Arnett as saying.
"But because her staff members were also waiting with us, we felt she was ultimately going to get there," he added. Rihanna later rued on Twitter: "This Chicago traffic is not working." She even praised the school's efforts.
"Barrington High School facts! They raised 40,000 dollars for Joplin Missouri after the tragic tornado hit Missouri in May last year... BHS Thank you man!!! You guys rule! I love this school," she tweeted.
She stayed at the school for just 12 minutes, got photographs clicked with the young fans and distributed tour tickets and left.
Spotted: Lara Dutta, Mahesh Bhupathi with their daughter in Bandra
Photos: SRK, Tamannaah Bhatia, Varun Dhawan at Mehboob Studio
Birthday special: Sushant Singh Rajput's journey from TV to films
Photos: Vibrant Sonakshi Sinha opens LFW 2017 on a cruise ship
Health in pictures: 8 reasons why people have unprotected sex