Seeing and talking to people of the dead is one thing, but all she could do was see them. Carri Brennan couldn't hear, or feel, or help them in any way. All she could do was watch and then walk away.
Melinda found out about Carri, once she had moved into Grandview and noticed a ghost tracking her every step. Melinda watched as Carri encouraged the ghost, but made no motion into helping him. What was her deal?
When Melinda and Carri start getting along later on, Carri meets Eli James, the one who could only hear ghosts. Maybe that's why they get along so well. Carri can only see them, Eli can only hear them, and Melinda can do both!
...It turns out that the ghost haunting Carri was none other than Rick Payne.