<< When she arrived, she called home and said the back of the van was
covered with oil. Anyone have an idea as to what may have caused this &
what I can tell her to look for? From what she said, the oil covers the
glass all the way to the bumper.>>

Ray,
Anything that requires a petroleum product to function could be leaking
and blowing to the back end of the Van in the back draft.

To just pinpoint the leak over the internet without actually looking at
the vehicle in question at best a guess and would be actually
impossible.

Do some crawling under the back 1/4 of the Van.
If it's loosing oil bad enough to
cover the back hatch and window, you soon locate it.