Claudia Macri was insulted and spat at by the four girls and then kicked and punched after she followed them in the busy underground station, Rome's city council said in a statement.
A passer-by intervened and held two of the attackers, while another was caught by the warden and the fourth escaped.
Macri told Il Messaggero newspaper that she also suspected the teenagers of robbing passengers.
“I tried to warn the passengers, I shouted in English ‘watch out for pickpockets!’” she said.
The girls were later captured after they were indentified by a group of tourists for allegedly stealing €500 in cash, four credit cards and a camera. A court has ordered for them to be sent to a youth rehabilitation centre.
Ignazio Marino, Rome's mayor, praised Macri for her commitment, courage and determination, and described the attack as "unacceptable", Il Messaggero said.