"We have finished writing it. We have an official first draft," Lawrence said on BBC 6 Music.
The comedy film is about two sisters, which will be played by Lawrence and Schumer.
Meanwhile Lawrence has revealed the pair have a "life plan" to grow old together on an urbanised island like Martha's Vineyard.
The 'Silver Linings Playbook' star praised her close A-list pals, Amy, Adele and Emma Stone, and admits she feels more "normal" when they're around.
She told Glamour magazine: "I love Emma. She cracks me up; she's so 'theater.' She's so adorable. And Adele and I met, like, a year or so ago. Adele and I are a bit harsher; Emma's never had a bad thought about anybody in her life.
"It's so weird; I don't like new people. But these two women - and Amy - they're really lovely. And they're so normal.
"I feel like I'm hanging out with my friends - my friends that don't give a f**k about what I do ... Amy's always wanted to live on Martha's Vineyard, and we saw this house, and we're like, 'This is where we're gonna Grey Gardens, and we're gonna grow old and crazy together.' That's our life plan."
Meanwhile, the 25-year-old actress previously revealed Adele picked up the bill when the two of them went out with Emma Stone.
She shared: "Oh God, I don't know who picked up the check. It might've been Adele.
"I think we would've all been like, 'Adele, you've had a pretty good week.' So I'm sure we would've probably let her get it."
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