When many photography courses require a "fully manual' film camera, that can mean one of two different things:
- A film camera capable of being operated manually, even if the camera can also be used in automatic or semi-automatic modes.
- A film camera that can only be operated manually and has no capability of using automatic or semi-automatic modes.
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 could 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 as KEH who specializes in used gear only.
The Canon AE-1 and AE-1P offer some automatic exposure control as well as full manual control. Canon FD mount lenses used by the Canon AE-1/AE-1P are still reasonably plentiful and relatively easy to find on the used market.
The AE-1/AE-1P are powered by either a single 6V 4SR44 battery (various manufacturers have different numbers for it) or by 4 1.5V LR44 batteries. The LR44 button cells are still fairly common and relatively inexpensive. Major brick and mortar retailers sell them as they are used in a wide variety of devices from meat thermometers to wristwatches. The single 6V varieties are mostly carried only by specialty camera stores but are fairly easy to find online. Without batteries the AE-1/AE-1P are not operable. The horizontal cloth shutter curtains of the AE-1/AE-1P have not aged quite as well as the vertical travel metal shutters found on some other film cameras from the same era, but there are still many around that are in great shape. Of note is that the AE-1/AE-1P offered shutter priority auto-exposure but not aperture priority AE at a time when most AE cameras were the opposite - they offered aperture priority but not shutter priority. The only way to manually select the aperture with an AE-1/AE-1P is to use manual exposure mode. On the other hand, one could fully control the shutter speed and let the camera calculate the needed aperture.
The Nikon FM2 is a manual exposure only camera. Nikon F-mount lenses compatible with the FM2 are also plentiful, though one must be careful because although they will mount on older F-mount film cameras, some newer types of F-mount lenses introduced from around the year 2000 will not be fully functional with the older F-mount film cameras.
From Wikipedia (italics added):
The FM2 accepts all Nikon F bayonet mount lenses that support the Automatic Indexing (AI) feature introduced in 1977. The Nikon-made AI lenses of this type are the AF-S Nikkor, AF-I Nikkor, AF Nikkor D, AF Nikkor, Nikkor AI-S, Nikkor AI and Nikon Series E lenses (not to be confused with the more recent electronic AF Nikkor E type Nikkor lenses). Nikon’s most recent 35mm film SLR lenses, the AF Nikkor G type (introduced in 2000) and the AF Nikkor DX type (2003) will mount but will not function properly.
The Nikon FM2 is powered by either one 3V CR1/3N lithium battery, or two 1.55V SR44 silver-oxide batteries, or two 1.5V LR44 alkaline batteries. As mentioned above, LR44 and equivalent batteries are still very common and readily available at many retailers. The CR1/3N is used today in the collar of several popular "electronic fences" for pets, and many pet stores carry them. They're also readily available online and are also relatively inexpensive. FM2 bodies will operate without a battery (except for the light meter). Technically, FM2 bodies made after 1984 are FM2n models, but the only external difference on the camera body is the red 1/250 second shutter speed marking denoting the flash sync speed. The original 1982-84 FM2 bodies had a different shutter mechanism and the flash sync speed was 1/200 second.
The Pentax K1000 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. Without a battery everything except the light meter still works and photos can still be taken at every available aperture and shutter time setting.
From the above it should be clear that availability of batteries and lenses that fit a particular camera, along with shutter durability, are things that should figure high on the list when buying an older used film camera.
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.
When I look at my digital camera, I can set things like ISO, aperture, etc. If I look at something like the Canon AE-1, it only has a single dial with what looks like a single ISO.
The large control dial on the AE-1 is the shutter speed control. The ASA (ISO setting is incorporated into this dial and visible through a small window in the dial. As mentioned above, the AE-1/AE-1P was a "shutter priority" (Tv or S mode on your digital) camera at a time when most semi-automatic cameras were "aperture priority" (Av or A mode on your digital camera).
Most film cameras leave the aperture setting to a ring on the lens, rather than placing it on the camera body. If a camera has automatic modes where the camera selects the aperture, the lens will have an "A" (for Auto) or similarly named position on the aperture ring that allows the camera to set the aperture via a mechanical linkage.
Related questions here at Photography SE:
I'm getting started in photography and taking a photography class — what camera should I buy?
Is a Pentax K1000 relevant today, and how can I get the best use of it?
Is a Nikon FG good enough for art school?
What considerations should be made for choosing a manual film SLR for photography classes?
For after the course:
Even if she decides she wants to ultimately shoot with film, shooting with a slightly older used digital camera is a faster and more economical way to improve with many of the fundamentals of photography, including exposure, composition, technique, and how using different focal lengths, apertures, shutter times, etc. will affect the resulting image than starting out with a film camera would be. This is particularly the case when one might not be sure if any problems one might see in one's earliest images are the result of user error or of camera malfunction.
For more along those lines, please see:
With which film camera should I start?
Should I continue to learn exposure on a film camera or switch to digital?