She's not a serious revolutionary (7)

I believe the answer is:

mildred

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'a serious revolutionary' is the definition.
The definition suggests a singular noun which matches the answer.

'she's not' is the wordplay.
'she' becomes 'Mil'.
'not' becomes 'dred' (I am not sure about this - if you are sure you should believe this answer much more).
'mil'+'dred'='MILDRED'

Can you help me to learn more?

(Other definitions for mildred that I've seen before include "lady?" , "Woman" , "Girl" .)

I've seen this clue in the Evening Standard.

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