Ghost Or Imagination?

In my opinion, they are all  Cadence's imagination because many details in the book shows us that they are only exist in where Cadence shows up. However, many people say that they are ghost and only Cadence can see them. I believe that they are not ghost. For example, " The liars don't come to the dock when we pull in, and neither do Aunt Bess and Grandad" (Lockhart 65). As we all know, Gat, Johnny and Mirren are all her best friends, so they would love to welcome Cadence to come back. However, they didn't; if they are ghost, Cadence should saw them, so the truth is that they are all her imagination. Another example, " I open the laptop. Do a search and find all the notes addressed to her" (Lockhart 187). If they are all ghost, they should be able to open the email, but the truth is that Cadence opened the email by herself read by herself. I also find out that Mirren, Gat and Johnny always repeat what Cadence's mother told Cadence which means they don't have all the information either and they don't have their individual thought. Hat they told Cadence is what Cadence is trying to tell herself.