Earlier this year, the actor revealed that her youngest child, whom she shares with husband Christopher Guest, is a transgender woman.
Ruby, who admits she knew she was "different" her entire life, is now opening up about her journey for the first time — and how Jamie has been by her side every step of the way.
Although Ruby says she struggled to come out to her family and ended up doing so via text message, she says she was met with overwhelming support.
"It was scary — just the sheer fact of telling them something about me they didn't know. It was intimidating — but I wasn't worried. They had been so accepting of me my entire life," Ruby told People.
Meanwhile, Jamie, who admits she didn't have an "inkling" that Ruby was trans, added that her daughter's journey has been an important learning experience.
"It's speaking a new language. It's learning new terminology and words. I am new at it. I am not someone who is pretending to know much about it. And I'm going to blow it, I'm going to make mistakes. I would like to try to avoid making big mistakes," Jamie said.
She continued, "You slow your speech down a little. You become a little more mindful about what you're saying. How you're saying it. You still mess up, I've messed up today twice. We're human."
Jamie admits that the most difficult part of Ruby's transition for her has been letting go of old habits, like calling her daughter by her dead name, even though she agrees that it "so doesn't fit anymore."
Ruby says she "doesn't get mad" about the accidental slips and, above all, hopes that she can help others who are going through the same thing.
"I'm not proselytizing, and I'm not trying to force-feed something to people. I'm simply saying, 'This is our family's experience.' I am here to support Ruby. That is my job. Just as it is to care and love and support her older sister Annie in her journeys. I'm a grateful student. I'm learning so much from Ruby. The conversation is ongoing," Jamie said.
She concluded, "If one person reads this, sees a picture of Ruby and me and says, 'I feel free to say this is who I am,' then it's worth it."