It's been a long time since I tried Elements but if it has a measure tool (under the eye dropper tool in
PS) try the following.
Drag the Measure tool along the top or bottom edge of the image (not the canvas). You can also choose a vertical line. Then go to the Image menu and select Image>Rotate Canvas>Arbitrary. When the dialog box comes up it will show you an angle. Just hit the enter key and Elements should automatically straighten the image.
Regards, Murray