What computer operating system for your Premiere Elements 13?
If Windows, you have two possibilities...
1. Export the Timeline of project 1 to a file saved to the computer hard drive. Then import that export into project 2.
Assure that the project settings and export settings are consistent from project to project. A popular choice for the saved file is Lagarith.avi (after you download and install the Lagarith video codec, it should be available to you under Publish+Share/Computer/AVI and the selected preset's Advanced Button/Video Tab).
2. Use ClipMate in conjunction with Premiere Elements for a copy/paste insert from project 1 to project 2.
Any questions or need clarification, please do not hesitate to ask.