Tossed her in river (5)
I believe the answer is:
rhine
'river' is the definition.
(Rhine is an example)
'tossed her in' is the wordplay.
'tossed' indicates anagramming the letters.
'her'+'in'='herin'
'herin' is an anagram of 'RHINE'.
(Other definitions for rhine that I've seen before include "Great river in Germany with Lorelei Rock" , "Bonn's river" , "Great German river with Lorelei Rock" , "Cologne's river" , "valley" .)