A 9-year-old girl suffered serious burns after accidentally setting herself on fire with a lighter at her Brooklyn school Wednesday, according to sources. The girl was playing with a lighter she’d found in the third-floor bathroom at Excellence Girls Charter School in Bedford-Stuyvesant when her school uniform went up in flames around 2:30 p.m., sources said. School officials called 911 after the victim began screaming, sources said. She was taken to the burn center at NewYork-Presbyterian/Weill Cornell in Manhattan with second- and third-degree burns to 40% of her upper body. The girl is currently in stable condition. No one else was injured.