Member of educational order — Charity Pecksniff perhaps? (6,2,5)

I believe the answer is:

sister of mercy

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'charity pecksniff perhaps?' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'member of educational order' is the wordplay.
'member' becomes 'sister' (sister is a kind of member).
'educational order' becomes 'mercy' (I can't explain this - if you can you should believe this answer much more).
'sister'+'of'+'mercy'='SISTER OF MERCY'

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I've seen this clue in The Times.

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