Girl's well after setback, praise be! (7)
I believe the answer is:
hosanna
'praise be' is the definition.
(I've seen this before)
'girl's well after setback' is the wordplay.
'girl' becomes 'annas' (I can't explain this - if you can you should give a lot more credence to this answer).
'well' becomes 'oh' (both are exclamations of surprise).
'after setback' is a reversal indicator.
'annas'+'oh'='annasoh'
'annasoh' back-to-front is 'HOSANNA'.
Can you help me to learn more?
(Other definitions for hosanna that I've seen before include "shout in adoration" , "Shout of acclamation" , "Adoring cry" , "Hebrew word in the Bible, an exclamation of praise" , "exclamation of joy" .)