Oddly, spy I love is a girl (6)
I believe the answer is:
sylvia
'girl' is the definition.
'oddly spy i love is a' is the wordplay.
'oddly' means one should take alternating letters.
'spy'+'i'+'love'+'is'='spyiloveis'
The alternate letters of 'spyiloveis' are 'sylvi'.
'sylvi'+'a'='SYLVIA'
(Other definitions for sylvia that I've seen before include "American poet, 1932-63" , "Girl's name" .)