In Route 28, a woman in a house says the following lines, 'Oh, dear. You found me. Please don't tell anyone about me. I'll give you this for keeping my secret. Please? ' Then she gives the player TM47, and if you talk to her a bit more... 'It's tough being a celebrity. Everywhere I go, people chase me. I just want to be left alone...' Here's some proof: Go from 2:14 onwards.
Seeing as she used to be a celebrity and is now hiding away, she could be a female character from RGBYFRLG that disappeared in later generations (Lorelei, Agatha, even Leaf).
Do you think this could be a secet cameo of Lorelei?