Going back and looking at the timeline of CP and Carolyn's online communications, along with Jamie's statement that he last saw Erica in November 2011, I absolutely believe that the adoptive parents got rid of Erica in November.
Online contact began in April 2010. when CP contacted Carolyn via Facebook.
CP did not want SP to know she and Carolyn were communicating.
Jan. 5, 2011 is the only time that Carolyn met Erica, along with the adoptive parents, at the What-A-Burger in Mooresville. Carolyn states that Erica's arm was in a cast and sling. (The medical records, if Erica had been treated, would back up Carolyn's recollection. Also, if CP didn't want SP knowing that she and Carolyn were communicating why was SP at this meeting? What would have changed?)
The next day, Jan. 6, Carolyn writes that someone has told her on social media what a bad mother she is, but states it was not one of her children who said this.
Feb. 2011, A message was sent to Carolyn from CP's account. The sender said she was Erica and she didn't want any more contact with Carolyn. Asked that Carolyn not write to CP again.
Nov. 2011. CP told Carolyn that Erica went camping with Tammy, CP's sister.
More than a year passed before the next time CP responded to Carolyn's messages, in Jan. 2013.
(So, CP tells Jamie in November 2011 that Erica is with her "Nan" and tells Carolyn in November 2011 that Erica has gone camping with CP's sister. Then there is no further response from CP to Carolyn's messages.)
Feb. 2013. CP says she's not sure why "all these rumors are floating around about where she is." CP goes on to say Erica has spent some time with CP's aunt who is helping the teen with her homework.
Mar. 2013. CP messaged Carolyn for the last time and said Erica and Brooke are in Asheville with CP's aunt.
(Does CP even have an aunt in Asheville. Seems pretty similar to a "Nan".)
Many thanks to ACR for the timeline where I read the preceding information and loosely set these thoughts, in blue, together.