Hi Ben
In the preferences dialog, under the External Editing tab, is Elements listed as an additional external editor? If so, you can clear it here.
Otherwise, try looking in the "External Editor Presets" folder to see if you have a file for Elements. If you do, delete the file. On a PC the folder should be located at Users\YourName\AppData\Roaming\Adobe\Lightroom\External Editor Presets.