That guilelessness worked in her favour. For the audience, it often felt like watching your cool older sister (or your precocious young daughter) up on stage, rather than some untouchable pop star.
What's more, Rodrigo needed none of the usual pop star props. There was no choreography. Until the encore, there was only one costume. All she required were the songs and her pin-sharp, all-female band.
She charmed the audience even more as she introduced the new wavey So American – a song about the inside jokes she shared with an English boyfriend.
"I love England so much," she said. "I love how nobody judges you for having a pint at noon. I love English sweets, all the sweets from M&S, Colin the Caterpillar specifically.
"True story: I have had three sticky toffee puddings since coming to Glastonbury. And as luck would have it, I love English boys."
England loved her right back, saving their biggest reaction for her encore – a headlong rush through Brutal, All American Bitch, Good 4 U and Get Him Back.
She left the stage under a downpour of fireworks, as inflatable balls bounced around the audience and our ears rang with feedback.
It was, hands down, the best (and best-attended) headline set of the weekend.
Olivia Rodrigo had understood the brief: Bring the hits. Make it unique. And make it personal.
Perhaps she'd learned that from Jarvis Cocker, whom she'd watched from her boyfriend's shoulders on Saturday.
"To enjoy Glastonbury, you have to submit to it," he advised.
Rodrigo channeled that spirit innately. She's welcome back any time.