Girl with star in US city (3,5)
I believe the answer is:
las vegas
'us city' is the definition.
(I've seen this before)
'girl with star' is the wordplay.
'girl' becomes 'lass' (lass can informally mean a girl).
'with' means one lot of letters goes inside another.
'star' becomes 'Vega' (star in the constellation Lyra).
'lass' enclosing 'vega' is 'LAS VEGAS'.
'in' is the link.
(Other definitions for las vegas that I've seen before include "Nevada's largest city" , "US gambling city" , "US gambling centre" , "Gambling city in Nevada, USA" , "Sin City, USA" .)