What computer operating system is your Premiere Elements 12 running on? Have you updated from 12 to 12.1 Update via a project's Help Menu/Update? If not, please do so. That is all background information for now.
As for the question that you are posting....
I think we need to go a lot deeper into what you are doing. Here are some considerations
The aspect ratio setting is in the import settings. In Premiere Elements 12 Expert workspace, the project automatically sets the project preset based on the properties of the first video file that you drag to the Expert workspace Timeline. If your video's properties include a 16:9 flag, then the project settings will have a 16:9 flag (aspect ratio). If you do not want the project to set the project settings automatically, you can set the project settings yourself manually with File Menu/New/Project and then import your source video.
If a problem exists where imported 16:9 video is presenting in Premiere Elements as 4:3 instead of 16:9 (typical of the JVC .mod file issue), then you can set the pixel aspect ratio under Interpret Footage feature inside the project workspace.
At this point, I think it best for you to give more details and background behind your question so that we can be sure that we are giving you the information that you need to succeed in your projects.
If you need clarification on anything written, please do not hesitate to ask for clarification.