The second transformation was much more gruesome:  
There are two mythological ladies with this name. One cut off a golden hair from her father's head, and as punishment was changed into a lark.  The second transformation was much more gruesome:  she was a nymph who fell in love with Glaucus. This angered Circe, who changed her into a monster with twelve feet, and six heads that barked like a dog. FTP identify this name and you will have identified one of the guardians of the Straits of Messina.
There are two mythological ladies with this name. One cut off a golden hair from her father's head, and as punishment was changed into a lark.  
Scylla