Just the girl for an excursion (5)
I believe the answer is:
sally
'for an excursion' is the definition.
(I've seen this before)
'just the girl' is the wordplay.
I cannot quite see how this works, but
'girl' could be 'ally' and 'ally' is found within the answer.
A single letter 's' remains 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 sally that I've seen before include "one in 3 the 12 30 [DROP the DEAD DONKEY]" , "Set out - girl's name" , "Sortie; witty retort" , "army" , "excursion" .)