You could try entering devmodeon in a search and then trying the factory reset from the Developer Options menu ( More => Settings =>Device information => Developer options ). This is the old factory reset reverting to factory firmware and wiping everything.
You can also trigger a manual factory reset by connecting your Aura One to power (computer or wall wart), holding the power button until the Aura One turns off. Once it has turned off, press and hold the power button until the Restoring screen shows and then release the power button.
Out of curiosity, how are you trying to uninstall NickelMenu? If you are placing a file called uninstall in the .adds/nm directory, if your Kobo eReader.conf contains the correct ExcludeSyncFolders line under the [FeatureSettings] header, Nickel should not even be scanning the nm folder (I use the second line since I rename the screensaver directory to screensaver_old when I turn off the using the screensaver directory to allow showing cover instead).
Code:
ExcludeSyncFolders=(\\.(?!kobo|adobe).+|([^.][^/]*/)+\\..+)
ExcludeSyncFolders=(\\.(?!kobo|adobe).+|([^.][^/]*/)+\\..+)|(screensaver_old)