You would need to have her tested at UC Davis to be sure, but from what I see of her in those photos, she looks like a sabino to me. When it is minimally expressed, Sabinos don't always look very different from other horses with socks and a blaze. They just seem to have a bit more "crome" than most. One quick difference between sabinos and horses that simply have socks and a blaze, however, is that their facial markings tend to be crooked and the wite on the legs form a sharp point. Since it can be so subtle, it can remain latent in many breeds for many generations, present but unrecognized, until the right stallion and mare come together to produce a foal with a bald face, blue eyes, white all the way up the legs, and a large belly spot. This explains why it has remained "hidden" in pure Arabians for so long.
Interestingly, prejudice against Sabino Arabians might have once had a practical value. In extremely hot and sandy regions, such as the deserts of the Middle East where Arabians originate, horses with white skin on their legs sometimes suffered from a condition known in our tongue as "sand scald". Heat reflected up from light colored sand would burn the legs, much like a sunburn but a little worse. The sand itself would further irritate the wound. Horses with this painful condition were less useful than horses that did not. So, many breeders favored horses with no white feet in their breeding programs, thus reducing the frequency of sabino in the breed. However, in other Arabic sub-cultures, horses with white feet were considered to be good luck and others paid no heed to the color of a horse at all, so long as it was rugged, fleet, and sound, so the sabino gene was not wiped from the breed entirely.
Old artifacts and paintings from Persia show Arabian horses that were white all over except for a strip of colored area along the spine (giving them colored manes, tails, and a broad colored area across the back, rump, and croup). Many people considered this to be artistic license until we gained a better understanding of the sabino gene. Many horses with maximal expression of sabino look very similar to the horses in the ancient art. It is now being used by some to show the sabino gene has always existed within the purebred Arabian gene pool.
Many sabino Arabians in North America can trace their ancestry back to the famous bay stallion Khemosabi, who is himself a grand example of how sabino can be disguised as ordinary markings on a solid horse. If DNA testing proves that your mare is a Sabino Arabian, it may be interesting to look at her pedigree to see whether she includes any Khemosabi blood. Khartoon Klassic is descended from Khemosabi.