The background image is an option already User->Policies->Admin Templates->Desktop->Desktop->Desktop Wallpaper.
The desktop color is not however, you'll need to create an ADM file an import it.
Here's the file I use:
CLASS USER
CATEGORY "Desktop"
CATEGORY "Custom"
KEYNAME "Control Panel\Colors"
POLICY "Background color"
EXPLAIN "Allow you to control the background color of the user's desktop."
PART "Enter the RGB values of the user's desktop background (ex: 128 128 128)" TEXT
END PART
PART "Color" EDITTEXT
REQUIRED
VALUENAME "Background"
END PART
END POLICY
END CATEGORY
END CATEGORY
Open notepad, pop that in, save it as something reasonable with the file extension .ADM
Open the GPO, right click Admin Templates, Add, Add..., Find the file, Close. Find the setting in User->Admin Templates->Classic Admin Temp(if on Vista or Win7)->Desktop->Custom->Background Color
Note: Since this GPO is processed after the user logs in, and after Windows sets the background color, the first time the user logs in they will default to whatever the machine's default background color is. I've never been motivated enough to write the ADM file to set the default background color, though it should be possible. In any case, the second login and forward the color will be set correctly. This is due to how MS implemented the background color setting in the registry. Also, after this GPO is removed the user will retain the color, it will not revert as with most GPO settings; again it's how MS chose to implement the setting...
You can try to run gpupdate as admin if you have not tried that.
Software restriction policies do not apply when Windows is started in Safe Mode. You can run gpupdate in Safe Mode to refresh the software restriction GPO.
Best Answer
As far as I know, deleting the GPO only removes the enforcement of the policy. That is, it won't reapply anymore and overwrite changes to the policy. If there is not another GPO which applies and alters those same settings, they won't be changed. Any non-default settings are NOT reset to defaults just because you deleted the policy.
The easiest way to fix this would be to use another policy to reapply the default settings, then remove that GPO once it has applied.
Edit: Apparently, according to this forum post, some settings will revert, and some will not. https://social.technet.microsoft.com/Forums/windows/en-US/41a9b71d-ef34-40cc-b071-4fbbfe61acba/delete-group-policy-removes-settings?forum=w7itprosecurity
I assumed in my initial answer that you had already done a 'gpupdate /force' and had her log off and back on. If not, you should try that before resorting to the dummy policy.