"I just I feel like crying," she said of being a first-time Academy Award nominee while on set of her sitcom, Mom. "It's a pretty fantastic thing to have happen in my life."
Janney said she was celebrating with family and friends even before she heard her named called early Tuesday morning. "It feels better than I ever thought it would or ever allowed myself to imagine it would be," she continued. "You know, thinking that you can't ever imagine that it'll happen for you, so you don't think about it too much, and now that it has, I feel just unbelievably happy."
Upon talking to ET, Janney had another celebratory moment when a bottle of Piper-Heidsieck champagne -- which is returning as the sole champagne brand poured at this year’s Oscars and Governors Ball -- was popped and exploded in what would have made for a perfect movie moment.
"That was the most incredible champagne cork pop I have ever [seen]!" she exclaimed. "Is everyone OK?"
Janney also shared that her Mom co-star, Anna Faris, sent her a "lovely text this morning," congratulating her on the nomination. The two will soon be celebrating their 100th episode of Mom, which airs Thursday nights on CBS.
The 58-year-old actress portrays Tonya Harding's estranged mother, LaVona Golden, in I, Tonya, and had a bird on her shoulder for many of the scenes. Upon accepting a Golden Globe for her role earlier this month, she even took the stage with a fake bird on her shoulder.
Janney told ET that her feathered friend -- which she referred to as "Little Man" -- was the "best actor animal co-star" she's ever had -- but will he be with her at the Oscars?
"I really wish," she quipped. "I don't think he would do well on the red carpet. I think he might just fly away."
Janney will be joined, however, by her co-star, Margot Robbie, who is also nominated for her lead role as Harding herself, and Tatiana S. Riegel, who is up for an Oscar for editing 'I, Tonya.' "I'm so happy for Margot and Tatiana," she said.
Janney was also thrilled that Octavia Spencer, her co-star from The Help, was nominated for her role in The Shape of Water, making her the only black actress to follow up an Oscar victory with two nominations. Spencer also ties with Viola Davis, another star of The Help, as the most nominated black actress in the Oscars' 90-year history.
"I'm so proud of Octavia," Janney said in praise of the 47-year-old actress. "I couldn't be more thrilled for her. ...Ever since the moment I met her, she's been one of my favorite people."
Catch Janney and Spencer at the 90th Annual Academy Awards, hosted by Jimmy Kimmel, when it airs live from the Dolby Theatre in Hollywood, California, on Sunday, March 4, 8:00 p.m. EST/5:00 p.m. PST on ABC.