I think I get why esper girl likes him. From what we can infer, she doesn't have many friends, and considering the fact that shes an esper, people probably see her as weird. Then comes this guy, who can not only see ghosts, he looks more comfortable around them than with other humans.
He's probably the only guy she's been around for an extended amount of time, and he's accepting of her quirks. That's probably a dream come true for her.