She has 180,000 followers on Twitter, became a daytime TV star with a cooking show sharing traditional convent recipes and waded into local politics speaking out in support of Catalan independence.
But the latest public declarations from the 51-year-old Dominican nun have provoked a stern telling off by the Catholic Church.
Her unlikely appearance on a chat show at the weekend to talk about sex led to her revealing that she didn't really believe in one of the tenets of the Roman Catholic faith – that Mary, mother of Jesus, was a virgin.
"I think that Mary was in love with Joseph and that they were a normal couple, and the normal thing is to have sex,” the nun who was born in Argentina before moving to a Catalan convent 26 years ago told Risto Mejideon on the Cuatro show Chester in Love.
"It's hard to believe and to take in,” she added. "We've stuck with rules that we have invented without reaching the true message.”
Her comments earned a quick rebuttal from the Bishop of Vic who issued a statement insisting that "in light of recent statements by a nun” he sought to remind those that the Catholic faith was clear on the subject of Mary's virginity.
"The belief that Mary was a perpetual virgin forms part of the faith of Church from its beginnings and that this truth of faith was collected and proclaimed by the Second Council of Constantinople, being the primary Marian dogma observed by Catholic and Orthodox Christians."
Sister Lucia, who lives in a convent in Manresa and has more than 180,000 followers on Twitter, also discussed her views on sex on the programme.
"Sex is a way of expressing feelings and love and forms a part of all people,” she said. "The Church has treated the subject as dirty and secret but I think it is a blessing”.
When asked if she herself had sexual needs and what she did about them, she replied: "Just as I told you that I have never had sex and am a virgin, I can tell you that I do not masturbate either.”