Claims about nurse seen in part of letter (8)
I believe the answer is:
pretends
'claims' is the definition.
(pretend can mean to falsely claim)
'about nurse seen in part of letter' is the wordplay.
'about' becomes 're' (common abbreviation for 'with reference to').
'nurse' becomes 'tend' (I've seen this before).
'seen in' means one lot of letters goes inside another.
'part of letter' becomes 'PS' (postscript written at the end of a letter).
're'+'tend'='retend'
'retend' inserted within 'ps' is 'PRETENDS'.
(Other definitions for pretends that I've seen before include "Lays claim" , "Shams" , "Plays make-believe" , "Postures" , "Feigns, dissembles" .)