Just wanted to let people know, I added a new page to The Hardy Boys Wiki about Mimi Morton.
http://hardyboys.wikia.com/wiki/Mimi_Morton
Nice. Good to have this new character documented on the Wiki. I may be wrong, but I believe Mimi has shown up in the Clue Book series too.
Even though I own all the Secret Files and Clue Books, I haven't read them all yet. But it's surprising she hasn't turned up in the Adventures or been mentioned.
I have a feeling this is a character who will only stay in the Secret Files/Clue Book continuity. I just don't see her being added to the Adventures continuity- I think that's kept as its own separate thing. And it's a bit jarring after 80 something years to have a heretofore unknown sibling suddenly added to mainstream continuity. (Though admittedly, I think that was lost with the Digests. It's hard for me to digest the UB and Adventures books as part of the mainstream continuity either.)