Nineteen months after she played to just 350 people in London, Kacey Musgraves is the first country star to sell out this renowned 5,000-plus seated venue since 2003. “It’s a milestone moment,” she marvels.

The crossover success of 2013’s Same Trailer, Different Park has won the smalltown Texan two Grammys but Musgraves is visibly awed by her surroundings. “This is the fanciest place I’ve ever been to,” she says. “How did they let me in?”

For all her down-to-earth charm, however, the 27-year-old, who’s been performing since she was just 13, has impenetrable polish. In homage to new album, Pageant Material, Musgraves’s “Rhinestone Revue” features a pink-tinsel-bedecked stage strewn with glitter balls and star-shaped lights, while her five-piece band – including pedal steel guitar – wear raspberry-hued suits edged by LED lights.

Musgraves is catwalk ready in a sequinned playsuit and blush skater skirt, and an impatient crowd melts as she coos through the easy, country-pop of Pageant Material and Biscuits, an MOR take on TLC’s No Scrubs and a bluesed-up version of Coldplay’s Yellow.

Vocally light and sweet, Musgraves packs a lyrical punch on heartbreak ballad Fine and life-affirming Follow Your Arrow. But alone on stage with her acoustic guitar, all the poise and practised smiles vanish. “In the light of the … insanity that’s been happening, I really appreciate you guys being brave and coming out,” Musgraves says, starting to cry. “I’m scared too.”

She admits to experiencing “new feelings of fear” at shows since the Paris attacks and performs a spine-tingling Merry Go Round, before giving herself permission to enjoy her big moment, dancing in light-up cowboy boots for a defiant version of Nancy Sinatra’s These Boots Were Made for Walkin’.

• At Country2Country, 3Arena, Dublin, 11 March (box office: +353 1819 8888); Clyde Auditorium, Glasgow, 12 March (0844 395 4000); O2 Arena, London, 13 March (0844 856 0202).