Crazed Marie Lewis, 27, sent a tarantula's skin to Freddie impersonator Billy West with a note saying: "I hope this scares you."
And she made abusive calls to his wife Susan, claiming the singer had slept with a string of women.
Unmarried Lewis became jealous of the 45-year-old rocker's "glamorous lifestyle" after seeing him perform live, a court heard.
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She turned up at every show and grabbed a front-row seat to sing along with hits such as A Kind Of Magic.
Then she tracked the singer - real name William Westmoreland - to his home in Fife, Scotland, and started calling day and night.
Prosecutor David Pinnell said: "She would phone his wife and tell him that he had been unfaithful with women all over the UK. "She sent the couple abusive letters and the skin of a tarantula spider."
At one gig, Lewis had to be restrained by bouncers as she tried to assault the singer on stage.
She then approached Mr Westmoreland - who has performed 3,000 times as the late Mercury - as he turned on a town's Christmas lights. He called the police.
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Lewis, of Ebbw Vale, South Wales, admitting three charges of harassment.
Jeff Jones, defending, told Cardiff Crown Court: "She acknowledges her behaviour was cruel, relentless and vile."
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Lewis was given a restraining order preventing her from approaching the couple.
A spokesman for the singer said later: "It's been awful. We hope that's the end of the matter."
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