What computer operating system is involved? For now, I will assume Premiere Elements 13/13.1 on Windows 7, 8, 8.1, or 10 64 bit.
The same principle exits whether your version is 13/13.1 or earlier version. That is, you export the Timeline content of project 1 through 13 each to a file saved to the computer hard drive and then import those exports into one grand project. In doing this, you keep the project settings and export settings consistent from project to project. Lagarith.avi or AVCHD.mp4 files can be used for this purpose.
Please detail the problem in Premiere Elements 13 that is preventing you from doing this workflow as you have done successfully in the past with other versions of Premiere Elements?
With the requested information, we can customize a reply to your situation.