Girl's name or a jewel (4)
I believe the answer is:
ruby
I believe this clue is a double definition.
'girl's name' is the first definition.
'a jewel' is the second definition.
(I know that ruby is a type of jewel)
(Other definitions for ruby that I've seen before include "Deep 6 across" , "Deep red - transparent gemstone" , "A red jewel" , "Completely" , "Vivid red" .)