A woman composes a note to Lady Hamilton (5)

I believe the answer is:

gemma

I'm a little stuck... Click here to teach me more about this clue!

'a woman composes a' is the definition.
I can't tell whether this definition defines the answer.

'note to lady hamilton' is the wordplay.
'note' becomes 'g' (musical note).
'to lady hamilton' becomes 'emma' (I've seen this in another clue).
'g'+'emma'='GEMMA'

Can you help me to learn more?

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

I've seen this clue in The Globe and Mail.

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