Basil , Dawson And Haru : Who is Olivia ?

Haru asked Basil and Dawson about the girl who's name Olivia , and Dawson told her that's the girl in their first case together .
Scene is from fan fiction "The returns of the great cat and mouse detective" of  
Haru (c) The Cat Returns
Basil and Dawson (c) The Great Mouse Detective 
Haru version mouse (c)  
Background (c) The Great Mouse Detective