Aggie was born as Agatha Emily Walden in 1948. She is 8 years old.
The film Madeline is set in 1956. Aggie appears in the film as Madeline's best friend and confident, who, in contrast to Vicki and a few others, is more sympathetic towards Madeline, even going so far as to heeding her friend's requests to look after herself as Madeline runs away for the circus, having nothing to lose after the death of her parents and thinking that it's all her fault that the school is closing and Aggie holds onto Madeline's hat when she runs away.
- Barring canonicity, she is one of the few characters to have her full name revealed, along with Miss Clavel and Madeline Fogg.