before 1973 (most likely)
Yvonne was a friend of Petunia Dursley. In 1991, she was considered as a replacement babysitter for Harry Potter when Arabella Figg broke her leg. Unfortunately for the Dursleys, she was on holiday in Majorca at the time, and they were forced to take Harry to the Zoo on Dudley Dursley's 11th birthday.
- Harry Potter and the Philosopher's Stone (Mentioned only)