Relative has rung the girl about money (10)
I believe the answer is:
stepfather
'girl about money' is the definition.
I can't judge whether this defines the answer.
'relative has rung' is the wordplay.
'relative' becomes 'father' (father is a kind of relative).
'has' means one lot of letters go next to another.
'rung' becomes 'step' (I've seen this before).
'father' after 'step' is 'STEPFATHER'.
'the' is the link.
Can you help me to learn more?
(Other definitions for stepfather that I've seen before include "alternative pop" , "replacing old man" , "mater's new chap?" , "not original pop?" .)