Young female star leaves Las Vegas (4)
I believe the answer is:
lass
'young female' is the definition.
'star leaves las vegas' is the wordplay.
'star' becomes 'Vega' (star in the constellation Lyra).
'leaves' indicates named letters should be taken away.
'las'+'vegas'='lasvegas'
'lasvegas' with 'vega' taken out is 'LASS'.
(Other definitions for lass that I've seen before include "Girl (of Richmond Hill?)" , "Scottish girl" , "Familiar form of address for female" , "Young woman (-. Eng.)" , "Damsel" .)