legendarypokemonjunkie17
Back in MY day...
They could have her come back when the gang is at the Moss Rock/Cold Rock to evolve Eevee.
If they do have her come back, which I hope they will, then it'll have to be at cold rock, they already passed Moss Rock with Cheryl in The Great Burmy Evolution Plan and in Vespiquen and the Amber Castle. I know the titles are a little off, but you get the idea. They passed moss rock a long time ago.