"The Wizard of Oz" star had three kids - actress and singer Liza Minnelli, actress Lorna Luft, and Joey Luft, who works predominantly behind the camera. And while all three siblings are still alive, Zellweger explained to the Los Angeles Times that she was torn about approaching them while preparing for the role.
"I wanted to reach out not to ask questions, except to maybe ask what they would like or hope to see," she shared. "I figured that whatever was for public consumption, they had already shared at this point. I could find that".
"I wouldn't dream of calling and asking: 'Hey, what else can you share here? Because that'd be so helpful.'" the star added. "To me, what they haven't shared is treasure and that belongs to them and that's where it should stay".
However, The "What/If" actress revealed she did try to reach out to Liza through a mutual friend, but it didn't work out. She also said that Lorna's brain tumour diagnosis meant she didn't feel it was appropriate to probe her about her late mother at the time.
"That was a time for her and her family, not for a stranger to approach her about things that ultimately don't matter, right?" she insisted.
"Judy" hits cinemas on September 27.