From the way you describe the course expectations, it sounds like you probably don't need to worry about this. Others with similar questions might. Although anecdotal, my personal experience has been that the latter is more often the case than the former. Instructors typically require this because it is impossible to tell from the images captured if a film camera was used in fully manual operation or if one of the automatic modes were used to produced the photographs a student submits for an assignment.
You need tocould check with the course instructor for a clarification on this point. All of the cameras you have listed in the question would meet the conditions of the first option above but one of the three you list would not meet the requirements of the second.
When buying any older film camera you should verify that it operates correctly and doesn't have any light leaks that could fog loaded film. You need to include time to do this no matter which camera you wind up buying. It just goes with the territory of buying used film cameras. Good reputable sources for used camera gear are national retailers such as B&H and Adorama, as well aas KEH who specializes in used gear only.
The Pentax K 1000K1000 is a manual exposure only camera. You'll likely find lenses for the Pentax 'K' mount more easily than for the Canon FD mount.
The Pentax K1000 is considered by many to be the archetypal "student" camera. I've actually seen a few course syllabi back in the 1990s where the K1000 was one of a very short list or even the only acceptable camera for the course. The examples made in Japan or Hong Kong between 1976 and 1990 are all metal. The ones made in China between 1990-97 have a plastic lid and bottom plate. All versions have a rubberized cloth horizontal shutter. The same readily available LR44 batteries mentioned above are required to operate the K1000's light meter are still readily available at major retail outlets. Without a battery everything except the light meter still works and photos can still be taken at every available aperture and shutter time setting. 'K' mount lenses are also very plentiful on the used market.
If she's allowed to have some auto-exposure capability the Canon AE-1 would be a good choice. If she must have a manual only camera the K1000 is hard to argue against but the Nikon FM2 is also very good. You can get LR44 batteries for all of them at Walmart, Dollar General, CVS, etc. Used K-mount and F-mount lenses are plentiful and affordable. FD lenses are also still fairly easy to find, though not quite to the extent of the K-mount or F-mount.