Silly arse is beginning to needle lady (7)
I believe the answer is:
nerissa
'lady' is the definition.
'silly arse is beginning to needle' is the wordplay.
'silly' is an anagram indicator.
'beginning to' suggests taking the first letters.
The initial letter of 'needle' is 'n'.
'arse'+'is'+'n'='arseisn'
'arseisn' is an anagram of 'NERISSA'.
(Other definitions for nerissa that I've seen before include "Portia's attendant" , "Lawyer's clerk apparently" , "Girl from Belmont" , "One working for Portia" , "Serving maid" .)