You solved it!
With your help, Steve was able to find all of Blue's Clues. We were able to learn that Blue's favorite memory with Steve was celebrating her birthday with Steve and with all her friends and family. Blue loved that day and will always cherish that memory forever.Steve is very happy that Blue sent him a letter and he'll also cherish his memories with Blue forever. Steve and Blue would also like to thank you for all your great detective work helping Steve solve Blue's Clues.
In case you don't have access to the school
In order to learn what the third clue could be, hold up your device to the room tag of the Hewitt Art Gallery. The room tag will look like this: 