I don't care it's an often-muddy female accessory (2,4)

I believe the answer is:

so what

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'i don't care' is the definition.
(I've seen this before)

'female accessory' is the wordplay.
'female' becomes 'sow' (female pig).
'accessory' becomes 'hat' (I've seen this before).
'sow'+'hat'='SO WHAT?'

'it's an often-muddy' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for so what that I've seen before include "It's unimportant, who cares" , "Does it matter?" , "I'm not interested" , "Does it make any difference" , "I don't care" .)

I've seen this clue in The Guardian.

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