"I'd want to say to her that this is not a dress rehearsal," Fonda told TV's "Access Hollywood."
"This is it," she said. "If you blow it, you don't get a second chance."
Although the 20-year-old actress has a reputation for chronic tardiness, Fonda said she was convinced it was a passing phase.
"She parties all the time ... you know she's young and she can get away with it," Fonda said. You know it's hard after a while to party very hard and work very hard. She'll learn that."
Despite the flaws Fonda blames on youth, she said she loves the young actress "dearly."
"She's Lindsay Lohan," Fonda said. "I just want to take her in my arms and hold her until she's grown up. She's so young, so young and she's so alone out there in the world in terms of structure and people to nurture her. She is so talented."