Why was Iva Toguri (Tokyo Rose) arrested for treason?

I was watching a biography about her life and it said that Iva Toguri, an american citizen, was Tokyo Rose and that she had a radio program during WWII in Japan. During this time she would transmit her message to the GIs and help the Allied prisoners of war. She was arrested after Japan surrendered because of treason?? I don't understand, because all I could see was a person being suportive of her country (USA) even though she was a Japanese American. If anything I thought she was patriotic, because she wouldn't give up her american citizenship. It probably has to do with the time it took place, but even for that time the cause of her arrest seems irrelevant and just stupid. She was pardoned during the 70s, but she pretty much wasted her life on a stupid thing that had no evidence or rational explanation. Does anyone know if there was something more to it??