Girl, Virginia, going round a loch (7)
I believe the answer is:
vanessa
'girl' is the definition.
'virginia going round a loch' is the wordplay.
'virginia' becomes 'va' (US state abbreviation).
'going round' indicates putting letters inside.
'loch' becomes 'ness' (I've seen this before).
'a'+'ness'='aness'
'va' placed around 'aness' is 'VANESSA'.
(Other definitions for vanessa that I've seen before include "Red admiral butterfly" , "Girl's name; red admiral, painted lady genus" , "Girl's name - butterfly genus" .)