If she'd never become famous she wouldn't have had a mental breakdown and she'd still be able to have a job and have normal conversations with other people
that's debatable. If she has a mental illness, even if she wasn't famous she could have developed it, although I think since her life wouldn't be that much stressful, she would have developed it later in life.
I can't believe Britney was selling more in 2011 in her 13th year of her career with absolutely slim to none promo which was TERRYBLE and it was spring time too.