The "Matilda" actress - who has been open about the experiences of child stars in the past - has weighed in on the "Toxic" hitmaker's ongoing legal battle to have her father Jamie Spears removed as her co-conservator.
"I have never met her, but I really feel like I keep thinking about her song, Overprotected, and I think that she really needs to be able to live her life for herself, because she hasn't for so long," Mara told Entertainment Tonight.
"She has been living a life under somebody else's control and that is terrible, and I think that is the truth for a lot of people who achieve that level of fame. They don't really have any freedom."
"But she didn't have any freedom because of paparazzi and because of what was done to her because of the conservatorship, so I think that we need to let her live her life because anybody would be chaffing under those restrictions, anybody would be struggling."
The 34-year-old star admitted she was lucky her family kept her grounded during her early fame and made sure she still "remained a child."
"It was very important to my family that I remained a child," she added. "So, I shared a room with my sister until we were, I think I was 14 and moved houses, and finally I got my own room."
"I went to Girl Scouts and I went to a public school. And also, where I grew up in Burbank, California, it's actually pretty common to be a child actor.
"A lot of my friends had been in commercials for restaurants, or clothing and things like that. And in some ways, there was kind of a hierarchy where it was cool to be in these commercials, and was not cool to be in those commercials, and people just kind of saw it as a hobby."