Seen inside, sheltering with female (3)
I believe the answer is:
ewe
'female' is the definition.
(female sheep)
'seen inside sheltering with' is the wordplay.
'inside' means to look at the middle letters.
'sheltering' is an insertion indicator.
'with' becomes 'w' (short for with).
The middle of 'seen' is 'ee'.
'ee' placed around 'w' is 'EWE'.
(Other definitions for ewe that I've seen before include "She'll provide material to knit" , "Wool producer" , "Wool supplier" , "Sheep found in sewer" , "Female on farm" .)