Kneeling-desk that is used by girl in Peru, oddly (4-4)
I believe the answer is:
prie-dieu
'kneeling-desk' is the definition.
(desk for kneeling on when praying)
'that is used by girl in peru oddly' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'used by' means one lot of letters go next to another.
'girl' becomes 'Di'.
'in' is an insertion indicator.
'oddly' indicates anagramming the letters.
'ie'+'di'='iedi'
'peru' anagrammed gives 'preu'.
'iedi' placed into 'preu' is 'PRIE-DIEU'.
(Other definitions for prie-dieu that I've seen before include "It's knelt on for prayer" , "I'd 1 rupee (anag) - prayer desk" , "Desk at which one kneels to pray" , "On which to kneel and pray" , "Piece of furniture used in praying" .)