She makes a promising start with a nobleman (5)
I believe the answer is:
pearl
'she' is the definition.
'a promising start with a nobleman' is the wordplay.
'start with' says to take the initial letters.
'a nobleman' becomes 'earl' (earl is a kind of nobleman).
The first letter of 'promising' is 'p'.
'p'+'earl'='PEARL'
'makes' acts as a link.
(Other definitions for pearl that I've seen before include "Gem from oyster" , "Off-white colour" , "Precious gem" , "Girl < , pretty" , "something highly valued" .)