The Golden Globe nominee, 38, penned an essay for The New York Times in which she empathized with Spears, 39, recounting her own attempts to navigate fame at a young age.
Her essay comes after Spears spoke in court on Wednesday, publicly addressing the effects of her conservatorship for the first time.
During the hearing, Spears was not questioned by her conservators’ lawyers, nor have they had the opportunity to rebut her allegations in court.
Spears spoke out against her conservators and family, including her father Jamie Spears, 68, who’s served as one of the conservators of her estate since she was first placed under the conservatorship in 2008.
Tamblyn, who began working as an actress at age 11, revealed how money put a strain on her relationship with her family as she felt like “everyone’s A.T.M.” Her parents managed her career until her late 20s, when she let them go.
The Sisterhood of the Traveling Pants actress recalled “family members” and “Hollywood creatives” openly discussing her weight in front of her.
“But as someone who has experienced a small taste of what Britney has gone through, I know that what she has done is a profoundly radical act – one that I hope will ripple through the bodies and bank accounts of women across industries for generations to come.
“We can’t unknow her truth now – as told in her own voice, not a voice that’s been written for her, curated for her, or projected onto her.
Following her court appearance on Wednesday, a source told PEOPLE that Spears was “very nervous” but “grateful” for the opportunity to speak in front of the judge.