The place at which we admit a girl (5)
I believe the answer is:
where
'the place at which' is the definition.
'where' can be an answer for 'the place' (I've seen this before). I am not sure about the rest of the definition.
'we admit a girl' is the wordplay.
'admit' indicates putting letters inside.
'a girl' becomes 'her' ('her' refers to a girl or woman).
'we' going around 'her' is 'WHERE'.
Can you help me to learn more?
(Other definitions for where that I've seen before include "a question of location" , "enquiry" , "At which point" , "A question of place?" , "In which position?" .)