“Maybe Louise says something that implies she doesn’t know it was Adam that gave it to her.
“Tbh in real life it would be immediately obvious that Louise isn’t the same Louise as before, just from little things like dress sense, food & drink preferences, memory recollection, knowing certain people and places etc.
“It will all fall apart to anyone that really knows her e.g Adam (sic).”
Sadly as Behind Her Eyes is a miniseries, there may not be an opportunity to explore the meaning behind the keychain in further detail.
Viewers had hoped for justice for Adele and Louise, and they wanted Rob to be caught out in the end.