On Instagram, the 25-year-old model and actor donned an opened, white collard shirt that was tied at the waist.
"In honor of my queen, I found my old baby one more time costume top. Also, I had a-cups back then and a bowl cut," she captioned the sultry pic.
Baldwin is the latest celebrity to offer support to Spears after the premiere of The New York Times Presents' "Framing Britney Spears" documentary which exposed the lengthy conservatorship battle the singer is in over control of her estate and finances.
The conservatorship -- a legal guardianship giving her father, Jamie Spears, control over her finances and everyday life -- sparked the "#FreeBritney" movement with fans calling for her to be released from the legal agreement.
Spears has been under the conservatorship since 2008 following the singer's viral 2007 meltdown that showed her taking an umbrella to a paparazzi's car.
The doc also explains how the appointed conservators have control over Spears' travel and mental health care.
Spears' father Jamie stepped down from his role as her personal conservator back in 2019 due to health issues and a professional conservator was temporarily put in his place.
The current legal case pertains to the control over Spears' estate. Last summer, it was reported that Spears is "strongly opposed" to her father resuming duties as her sole conservator, while it was later reported that the singer has requested her current temporary conservator, Jodi Montgomery, become permanent.
Spears' court-appointed attorney, Samuel D. Ingham III, hinted that Spears may seek termination of the conservatorship in the future.
"Without in any way waiving her right to seek termination of this conservatorship in the future, Britney would like Ms. Montgomery’s appointment as conservator of her person to be made permanent," Ingham wrote, according to the NY Times.
In November, a judge in the case declined to remove Jamie as the head of his daughter's estate. Although Bessemer Trust was added as a co-conservator. Then in December, the judge extended Montgomery's temporary role until September 2021.
Among dozens of celebrities voicing support for Spears, the singer's own boyfriend Sam Asghari spoke out against Jamie Spears on Instagram recently.
"Now it’s important for people to understand that I have zero respect for someone trying to control our relationship and constantly throwing obstacles our way," the personal trainer wrote on his Instagram Story. "In my opinion, Jamie is a total d--k. I won’t be going into details because I’ve always respected our privacy but at the same time I didn’t come to this country to not be able to express my opinion and freedom."
Fox News' Melissa Roberto contributed to this report.