She finally received rent, a personal morale-booster (3,4)
I believe the answer is:
ego trip
'a personal morale-booster' is the definition.
(boost for one's ego or morale)
'she finally received rent' is the wordplay.
'finally' suggests the final letters.
'received' becomes 'got' ('get' can be a synonym of 'receive').
'rent' becomes 'rip' (synonyms).
The final letter of 'she' is 'e'.
'e'+'got'+'rip'='EGO-TRIP'
(Other definitions for ego trip that I've seen before include "Action to inflate one's sense of self-importance" , "Activity devoted to boosting one's self-esteem" , "Self-serving activity" , "Activity boosting one's self-importance" , "that involves swelling of head?" .)