I guess i have to say that I do totally disagree about her singing a biographical song.
I should clarify that I don't think either song is literally or strictly autobiographical. As per the lyrics of "Don't Tell Mama," are we supposed to believe that Sally's mother actually thinks she's living in a convent in the southern part of France? As per the lyrics of "Mein Herr," are we supposed to believe that Sally has actually traveled the entire European continent, going from one lover to the next? Seems to me she's a bit too young to have done so :-) But all of that said, I do think both songs are definitely apropos to different aspects of Sally's character, so they very much illuminate her character even if they aren't strictly and literally autobiographical.