The 24-year-old was up for best new artiste, and scheduled to perform with Lukas Graham - but she was still a little star-struck.
“My mum was my date - and we were both sitting there fan-girling like, ‘Oh my God, that’s Adele! Don’t look! Don’t look!’”
Ballerini, it turns out, is not the sort of person who keeps her cool when she meets an idol.
“The first time I met Carrie Underwood was at the Opry, before I had a record deal,” she recalls.
“I was waiting backstage with a bunch of people to say hello and finally it was my turn.
“I was going to say something normal - but then I saw her and went “Girl! You got so much sooouul!”.
“Of all the things I could have said, that’s what I chose,” she grimaces. “It was very weird.”
Awkward celebrity encounters aside, Ballerini has been living in a fairytale for the last few years.
She released her debut album, The First Time, in 2015 and watched its first three singles go to number one on Billboard’s country airplay chart - an historic achievement for a female artiste.
The bubbly, vivacious melodies and autobiographical lyrics of Love Me Like You Mean It and Peter Pan won comparisons to Taylor Swift, who quickly befriended the artiste (she calls Ballerini her “little sis”) and invited her onto her world tour.
That led to her Grammy appearance and, at next week’s Country Music Association Awards, a nomination for female artiste of the year.
All told, it’s turned out pretty well for someone who was shunned by the establishment when she first arrived in Nashville.
“I was a new girl, on an independent label and those were two strikes against me. No-one would write with me.”
It turned out to be a blessing. Left to her own devices, Ballerini, whose first concert was Britney Spears, channelled her love of pop and R&B into the album, giving her songs a vitality and immediacy that’s sometimes missing from traditional country.
The star’s co-producer, Forest Glen Whitehead, even refers to her as a “country Beyonce”.
“I grew up on a farm in Eastern Tennessee and country is where my roots are,” explains the singer, “but I listen to rap and I listen to R&B and I love pop.
“I’ve always been open about that because, as a songwriter, I always want to make sure that I’m trying new things.”
Despite the strength of her singles, Ballerini still faced an uphill struggle in the insular world of country.
Her debut came out in the midst of what’s been called “tomato-gate”, where radio consultant Keith Hill advised stations not to play too many songs by women and not to play two women back to back.
“If you want to make ratings in country radio, take females out,” he told trade publication Country Radio Aircheck. “They’re just not the lettuce in our salad. The lettuce is Luke Bryan and Blake Shelton, Keith Urban and artistes like that. The tomatoes of our salad are the females.”
Like many others, Ballerini was perplexed by his comments.
“When you think of country music history obviously you have George Jones, Garth Brooks, George Strait - all these iconic males. But you cannot talk about the history of country music without Loretta Lynn, Dolly Parton, Shania Twain. I mean some of the biggest artistes in country music history are female.”
In the end, she thinks, the uproar over Hill’s comments helped her cause.
‘Love Me Like You Mean It’ was in the top five when tomato-gate came out - and I think radio stations went, ‘Well, watch this!’ and helped me get to number one.”
But how do you follow up such a successful debut? With great difficulty, says Ballerini.
“I didn’t know how to make my second record for a long time.
“The first one worked so well that I was like, ‘How do I make that record again?’ And then I realised I can’t. That’s not who I am anymore.”
The answer was simple: Write an album about the person she’s become - and luckily Ballerini had a lot of material to draw on. No more love songs?
Unapologetically, released recently, is the chronological story of the last two years, as the singer left behind a “gross break-up” and got engaged to fellow country singer Morgan Evans.
One of the first tracks is Miss Me More, a slinky stomp in which the singer describes how her ex-boyfriend slowly eroded her identity.
“I retired my red lipstick ‘cause you said you didn’t like it,” she sings. “I didn’t wear my high heel shoes / ‘Cause I couldn’t be taller than you.”
“In a lot of young relationships, you fall in love for the first time and you give every part of yourself to make it work,” she explains. “But sometimes, when it’s not treated right, that’s how you lose yourself.
“I think it’s really a beautiful moment when you get to the other side, and you’re looking in the mirror and you’re like, ‘Huh, I thought I was going to miss him but - actually - I miss me!’”
Ballerini says she found it easier to write those “super dark” lyrics than the love songs that close the album. In fact, she’s so bad at the soppy stuff that she came up with a track called I Hate Love Songs.
A pastiche of saccharine 1950s doo-wop hits, it opens with the lyric: “I hate Shakespeare and Gosling and cakes with white frosting.”
“Do I really hate Ryan Gosling? Lord no!” she screeches. “He’s a beautiful man!
“But I love that song. It talks about that heart and head battle. I don’t want to be a cliched person in love; but I kind of am turning into that.
“Then the next song [on the album] is Unapologetically, where it’s finally like I’m fully in love. I love the tension of those two together.”
Just don’t expect Ballerini to stop being star-struck as her own star rises.
“I still freak out when I’m around Carrie Underwood,” she laughs, “and now I see her all the time.”