The actress stars as the mother of Laura 'Little Voice' Hoff in a new West End production of Jim Cartwright's play, with the title role taken by former X Factor singer Diana Vickers.
Sharp told Metro: "Jim could never have predicted it when he wrote it but the play is a strong reply to all that.
"You might be able to mimic other styles but what's important is that you are true to who you are. You have to find your own voice."
She added of the new run: "[Cartwright] wanted to do a production for a long time but they couldn't do it until they found someone to play Little Voice. Jane Horrocks left such huge shoes to fill."
Horrocks played Little Voice in the 1998 movie adaptation of the play, which also starred Brenda Blethyn, Michael Caine and Ewan McGregor.