Simplify the following text for a Grade 15 native English-speaking person.
Original: When she was briefly imprisoned at Perm in 1918 , Princess Helena Petrovna , the wife of Anastasia 's distant cousin , Prince Ioann Konstantinovich of Russia , reported that a guard brought a girl who called herself Anastasia Romanova to her cell and asked if the girl was the daughter of the Tsar .
Simplified: When she was put in prison for a short time at Perm in 1918 , Princess Helena Petrovna , the wife of Anastasia 's distant cousin , Prince Ioann Konstantinovich of Russia , said that a guard took a girl who called herself Anastasia Romanova to her cell and asked her if the girl was the Tsar 's daughter .