The 18-year-old singer blamed "really unfair" editing and costume changes for her exit from the BBC One competition.
St Luce left the talent show last night (May 6) along with Hannah Berney after not receiving enough public votes.
"The comments of the judges play a big part in whether the public want to vote for you or not," she told The Sun.
"In my blind audition and the battle round the last comments people saw of me were negative, but the judges had said positive things.
"I thought that was really unfair and didn't make any sense. It's unprofessional. They didn't show my full performances or my comments - everyone else had their comments shown."
She also claimed that her outfit was changed at the last minute, saying: "It was hectic. I hadn't eaten all day - two meals were cooked for me but I wasn't able to have them. All this stuff affected my performance."
St Luce then alleged that a lot of her votes were not "getting through".
A BBC spokesperson said: "There were no reported issues. The vote was scrutinised and independently verified."
The Voice UK will continue next week when contestants from Team Tom Jones and Team will.i.am will perform live for the second time. Two acts from each team will leave the competition on Sunday (May 13), while they will also perform a track with their mentors.
The next live performance show will air on Saturday (May 12) at 6.10pm on BBC One.