She is sensibly hiding return of monster ... (6)
I believe the answer is:
nessie
'monster' is the definition.
(Nessie is an example)
'she is sensibly hiding return' is the wordplay.
'hiding' indicates the answer is hidden within the clue.
'return' shows that the letters should be reversed in order.
'eissen' is hidden in the letters of 'she is sensibly'.
'eissen' in reverse letter order is 'NESSIE'.
'of' is the link.
(Other definitions for nessie that I've seen before include "Scots loch monster (colloq.)" , "Nickname for a Scottish monster" , "Supposed loch monster" .)