UK Cypriot Nicola Lambrianos, from Buckhurst Hill, was invited by the Lithuanian entrant Monika Linkytė to join her backing singers.
Eurovision fan Ms Lambrianos had been keen to get tickets to the event.
“Now I don’t need a ticket, because I’m going to be on stage,” she said.
A part-time singer, Ms Lambrianos performs as an Adele tribute act – Adele Uncut – among other singing jobs.
She met the Lithuanian star through a friend, who is a vocal coach.
Ms Linkytė has represented Lithuania once before, finishing in seventh place in the 2015 contest.
Ms Lambrianos said: “I was at an open mic night and my friend said they wanted to introduce me to a Lithuanian pop star and it was Monika Linkytė – if you’re a massive Eurovision fan like me, you’ll remember her from 2015.
“I cheekily asked if she could get me a ticket to the show in Liverpool, and the following week she messaged saying I’d inspired her to compete and asked if I’d like to watch her perform at the first heat in Lithuania.
“Afterwards, she said, ‘I know you sing – I think you need to be on stage with me’, and that was it – she said, ‘I want you on this journey with us’.
Seven weeks later, and after several trips to and from Lithuania to compete in the elimination rounds, she is about to take the stage in Liverpool for the final round.They will be performing the song “Stay”, which includes the lyrics “čiūto tūto” often used in Lithuanian folk dances as magical incantations.
Asked if she had any connection to Lithuania, Ms Lambrianos said a relative had taken a DNA test and “we are about 1% Lithuanian”.
Her grandmother confirmed that a relative many generations back was Lithuanian.
The experience of competing so far had been “overwhelming” and the atmosphere in Liverpool was “electric”, she added.