As famous mother-in-law, I grumble the wrong way (5)
I believe the answer is:
naomi
'as famous mother-in-law' is the definition.
(mother-in-law of Ruth in the Bible)
'i grumble the wrong way' is the wordplay.
'grumble' becomes 'moan' (I've seen this before).
'the wrong way' says the letters should be written in reverse.
'i'+'moan'='imoan'
'imoan' reversed gives 'NAOMI'.
(Other definitions for naomi that I've seen before include "Biblical woman" , "- - Campbell, supermodel" , "-- Campbell, British model" , "Ruth's mother-in-law (Bible)" , "woman's name" .)