The 27-year-old actress was speaking on her reality TV show Lindsay, when she was confronted by her wellness coach AJ Johnson who asked if she had been drinking.
"I was not drinking," said Lindsay, growing visibly tense on camera.
Lindsay is confronted by her wellness coach in the latest episode
AJ had brought up the subject, saying that she had found wine in Lindsay's apartment and that she had spoken with the star's mother Dina.
"Your mum told me that you had been drinking," said AJ.
"What? The other night at dinner? When she was drinking?" asked Lindsay. "She's projecting on me."
"This is something I don't feel comfortable discussing on camera," she added. "I thought you, of all people, as a friend, would tell me that in private. I would have appreciated if you would have told me one-on-one first."
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Lindsay and her mother Dina
"You mad at me?" asked AJ. "No, I'm not mad," replied Lindsay.
The Mean Girls actress is then filmed leaving her coach and jetting off to Los Angeles for a week, where she refused to contact AJ and allow the trip to be filmed.
When she returned, Lindsay admitted to having had a drink a month earlier while she was dating someone who she didn't name.
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"I wasn't considering the fact that the person I was seeing does drink and yeah I had some wine," she confessed. "I had so much guilt. It's okay to admit it. It's really scary. It took me a bit to realise, but then I thought, 'why am I holding this in?'
"I screwed up. And that's okay. That's a part of life."
"I had so much guilt," admitted Lindsay
After her wellness coach left, Lindsay was filmed speaking candidly to the cameras about AJ and looked visibly vulnerable.
"She was a guiding light," said Lindsay. "I felt like she maybe disrespected me by asking me things on camera. All in all, she was a blessing in disguise."
The documentary-series, which is aired on Oprah Winfrey's network OWN, follows Lindsay's steps towards a full recovery, after she spent last summer in rehab.