Horton and five other people were attacked at Russell Square in London. The other victims, who were Australian, American, Israeli and British, suffered injuries but survived, according to Metropolitan Police Assistant Commissioner Mark Rowley.
The 19-year-old suspect was arrested and is now in police custody.
Horton began her career in education in the 1980s, The Guardian reports. She was the wife of Richard Wagner, a psychology professor at Florida State University. She and Wagner had planned to return to Tallahassee on Thursday.
“There are no words to express our heartache over this terrible tragedy,” FSU President John Thrasher said in a statement. “We are shocked that such senseless violence has touched our own FSU family, and we will do all we can to assist Professor Wagner and his loved ones.”