Swell girl's nurse (7)
I believe the answer is:
distend
'swell' is the definition.
(I know that distend is a more specific form of the action swell)
'girl's nurse' is the wordplay.
'girl' becomes 'dis' (I've seen this in other clues).
'nurse' becomes 'tend' (tend can mean to nurse or look after).
'dis'+'tend'='DISTEND'
(Other definitions for distend that I've seen before include "Stretch" , "Swell, expand" , "Cause to swell" , "Increase" , "Make you bulge" .)