Photoshop elements 9 won't close

Also in the same

~/Library/Preferences

delete the

Adobe Photoshop Elements 9 Paths

and

com.adobe.PhotoshopElements.plist

Has it always done that running on El Capitan or is this something recent?

Generally the first thing to do is reset the pse 9 preferences.

Usually one does that by holding down the Shift-Command-Option keys just after starting the launch of the pse 9 editor.

Keep holding the keys down until you get a dialog asking if you want to Delete the Adobe Photoshop Elements Settings File

Press Yes

In your case i would instead go to

~/Library/Preferences

and delete (Move to Trash) the

Adobe Photoshop Elements 9 Settings folder

The above is in your User Library and to see that Library click on your desktop, then click on the Go menu and hold down the Option key. Then click on the word Library. That's your User Library.