Happy girl almost eaten by rodent (7)
I believe the answer is:
radiant
'happy' is the definition.
(thesaurus)
'girl almost eaten by rodent' is the wordplay.
'girl almost' becomes 'dian' (I can't justify this - if you can you should give a lot more credence to this answer).
'eaten by' is an insertion indicator (inserted letters get eaten).
'rodent' becomes 'rat' (rat is a kind of rodent).
'dian' inserted into 'rat' is 'RADIANT'.
Can you help me to learn more?
(Other definitions for radiant that I've seen before include "Very conspicuous" , "Bright" , "'Glorious, shining (7)'" , "Straight line" , "looking happy" .)