At first, I've been with Karretch's causal loop/bootstrap paradox idea (after all, if time travel is still in its infancy, how come there's already a guide? Golly, I wonder who wrote it...) but now it seems like that couldn't possibly work out.
Eh, I still believe it. Grammy could possibly legit not tell it's Kaede and it's a fakeout by the author. However, she outright says "hold more secrets as you get older" as a subtle way of sending the message she understands something is going on and it's doubtful she wouldn't recognize her own granddaughter even grown up, looking like her mother and father mixed up and all that. As for young Kaede, they interacted for all of I'd guess at most half an hour. That's plenty of time (or lack thereof haha) for a 5-7 year old to forget a person without any lasting memories. Kaede seems that much of an airhead to me as a teen that it's easy to fathom as a child.
