The Seminole High School student told investigators that she removed earbuds from her ears when she arrived at the bus stop and noticed a man near her, Cannaday said.
Deputies said the two got into an altercation and the girl received superficial wounds on her arm and a cut on her abdomen.
The girl ran home, where a sibling called 911. She was taken to a hospital as a precaution, investigators said.
"She was actually quite amazing in this situation," Cannaday said. "The fact that she had the wherewithal to fight her way through it and flee is probably what credits her for not being injured more seriously."
Cannaday said investigators are still trying to determine what the girl was slashed with, saying that it was possibly a knife.
Seminole County Public Schools spokesman Michael Lawrence said the student attends a magnet program in the district.
"We ask that all our Casselberry families that have students (who) ride the bus, walk or bike to school to be extra vigilant this morning," Lawrence said.
Sterling Park Elementary School was placed under lockdown while deputies searched the area with K-9 units. The Sheriff's Office has increased patrols of the area.
The attacker, who remains at large, is described as tall and possibly black or Hispanic, deputies said.