A bird in her nest (4)
I believe the answer is:
erne
'a bird' is the definition.
(erne is a type of bird)
'in her nest' is the wordplay.
'in' says the answer is hidden in the clue.
'ERNE' can be found hidden inside 'her nest'.
(Other definitions for erne that I've seen before include "Flier" , "Large bird" , "European sea eagle" , "one that catches fish?" , "Irish river, loughs; sea bird" .)