Physical Description: Black hair

Family members: A son

Animagus: Dog (probably failed)

She was a patient in the Janus Thickey Ward for permanent spell damage at St Mungo's. She was admitted before Christmas 1995. Her face was covered in fur and she barked instead of speaking. It is possible that she remained there for the rest of her life. It is unknown what exactly happened to her but the effects are similar to consuming Polyjuice Potion prepared with animal DNA. Her Healer mentioned that her son would visit the night of Christmas Day.

Etymology
Agnes came from a Greek word (hangnē) meaning pure, holy or lamb.

Behind the Scenes
The description on Pottermore of what happens if an Animagus transformation fails makes it seem likely that this happened to Agnes.