Best, perhaps, granny's hairpiece (7)
I believe the answer is:
topknot
'hairpiece' is the definition.
(I've seen this before)
'best perhaps granny's' is the wordplay.
'best perhaps' becomes 'top' (top can mean the very best. I am not sure about the 'perhaps' bit.).
'granny' becomes 'knot' (I've seen this before).
'top'+'knot'='TOPKNOT'
Can you help me to learn more?
(Other definitions for topknot that I've seen before include "Piled up arrangement of hair on the head" , "Hair extension" , "Tuft or crest on crown of head" , "Crest of hair or ribbon on crown of head" , "Fish" .)