A former "Free Britney" enthusiast says she regrets publicly pushing to get Britney Spears out of her conservatorship ...

Jessica -- the former advocate who goes by the handle "realiteatv3" on TikTok -- joined us on "TMZ Live" Thursday ... and, we asked her how she feels about pushing for Britney to get out of the conservatorship after her DUI arrest last night.

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Jessica -- who has already opened up on TikTok about feeling the movement ultimately did more harm than good -- tells us she's been watching Britney's scary social media videos ... including the clip where she danced around with a pair of knives, and it's made her do a 180 on her previous position.

It's clear Britney needs a conservatorship, Jessica says ... though she thinks it's best if her family and friends aren't in charge of it.

We broke the story ... Britney was arrested Thursday night and taken to a hospital where her blood was drawn and tested for substances. Britney's telling people in her orbit she blew a .06 percent BAC -- below the legal limit in California. But, she can still be charged with a DUI if she was driving recklessly.

A source familiar with the investigation also tell us an unknown substance was found in Britney's car at the time of her arrest.

She has a court date set for May 4 ... and, at least one former "Free Britney" advocate wants the courts to take a more active role in her life moving forward.