The Original Sheila
These early shots show the original colour scheme for Sheila's ride, before being altered to a style more in keeping with the rest of the vehicles. It looks as though this design was in use well into development, since as well as the render of the buggy there are screenshots - minus debug information - of the Strider tearing around some of the levels.
Update!
This footge just in from youTube, showing a live feed of the original Sheila in action - not sure, but this may be a modification, rather than legitimate footage?