Millie Davis (born 6 December 2006 ) is a Canadian actress who played Ms. O / Big O in the TVOKids/PBS Kids series Odd Squad, Riley in the Amazon Prime television show Dino Dana, Summer in Wonder, and Gemma Hendrix in Orphan Black. Millie Davis (born 6 December 2006 ) is a Canadian actress who played Ms. O / Big O in the TVOKids/PBS Kids series Odd Squad, Riley in the Amazon Prime television show Dino Dana, Summer in Wonder, and Gemma Hendrix in Orphan Black.