Nikki Bella's injury is a bulging disc in her lower back but she may be dealing with other injuries. Nikki got an epidural shot this week to help with her back problems. Nikki said that she will continue with her neck rehab for the next few weeks but the rehab hasn't responded well.
She is scheduled to get an MRI at the end of this month to find out if she'll need to get neck surgery. If she has to get the surgery then that basically takes her out of WrestleMania since she'll be out of action for a long time. While she is legitimately injured, keep in mind that the real injury is being incorporated into Total Divas so the storyline version of the injury on the show may not be exactly what the real injury is.
She can't really contradict anything in the storyline or talk too much about her injury until the show airs because there is a confidentially clause for everyone that appears on the show. Nikki has been making some appearances for the company during her time away from WWE TV.