Nah, it's nothing suspicious. She's doing it. She loves ghosts, she's a occult otaku. Whatever happened between eps 2 and 3 that allowed Reiko to see the ghosts too made her really happy.

When she visited Wakaba's home, she brought some prized ghost photos (circled for easy identification) instead of something normal like rice crackers or barley tea. She's just weird.

It's the art style that makes you think she's up to no good. Everyone has those shifty eyes. Wakaba's are just larger so you don't notice it as much.