Show relative daughter, Joanna (7,5)

I believe the answer is:

concert grand

'joanna' is the definition.
(cockney rhyming slang for piano)

'show relative daughter' is the wordplay.
'show' becomes 'concert' (concert is a kind of show).
'relative' becomes 'gran' (short for grandmother).
'daughter' becomes 'd' (genealogical abbreviation).
'concert'+'gran'+'d'='CONCERT GRAND'

(Another definition for concert grand that I've seen is " Large piano".)

I've seen this clue in The Telegraph.

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