She's a treasure to mum (5)

I believe the answer is:

gemma

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'she's' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?

'a treasure to mum' is the wordplay.
'a treasure' becomes 'gem' (gem is a kind of treasure).
'to mum' becomes 'ma' (both can mean mother).
'gem'+'ma'='GEMMA'

Can you help me to learn more?

(Other definitions for gemma that I've seen before include "girl" , "Bud" , "Girl's name" .)

I've seen this clue in the Evening Standard.

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