Crossword Genius

A diminutive girl, my sis (5)

Ross

I believe the answer is:

missy

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

'a diminutive girl' is the definition.
'missy' can be an answer for 'girl' ('missy' can be a synonym of 'girl'). I am unsure of the 'a diminutive' bit.

'my sis' is the wordplay.
'my sis' can be anagrammed to 'MISSY'.
Though, I'm not sure how the anagram is indicated.

Can you help me to learn more?

I've seen this clue in the Evening Standard.
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