Rachel attended Media Day -- it's unlikely they'd let her be in the house early like that if they were planning to bring her back as a cast member... right?
I have no doubt she'll come back to host a competition or something like that, but I don't believe they'd make her a full time member again.
But the wall were the houseguests are has a picture of Rachel.
CBS let's a handful of reporters spend a few hours in the house so they can test out all the camera angles and things for the new house... plus they do it to promote the new season.