Girl from Welsh valley extremely down about leaving (5)
I believe the answer is:
rhoda
'girl' is the definition.
'from welsh valley extremely down about leaving' is the wordplay.
I cannot really understand how this works, but
'from' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
'down' could be 'd' and 'd' is present in the answer.
'about' could be 'a' (abbreviation in Chambers) and 'a' is found within the answer.
The remaining letters 'rh' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for rhoda that I've seen before include "Woman" , "Girl's name; hoard (anag.)" , "Fem. name; hoard (anag.)" , "Girl" .)