Donna, mistakes of this nature happen more often than you would imagine. In the early days of hand filled out standardized forms you have overworked local doctors whose mind is occupied with other problems while filling out forms. Later, copies are made at the city, county and state levels where transcribers minds are elsewhere while constantly copying forms into official record books or files. I have seen the same same type of mistake a couple of times before. I've seen death records where the age is quite different than if you figure it out from the birth and death dates. Its even more common on the US census record. I've seen records where people have been recorded as B when they are definitely W, and the reverse. These are just some of the amusing times that come up in genealogical research.
As you grandmother died in the 1920s, the original record usually can't be changed. Its been copied, microfilmed several times and digitally duplicated in several locations within the state and nationally, as well as several websites. For a fee, I believe you can have a supplemental or corrected form made and filed in the official record, but it probably won't officially replace the original and will be ated as a recent form. I've found several individuals for whom two versions of birth and death records exist, the first in the 1920s and the other dated decades later. Its more common on adoptions and corrected birth records, but not unheard of in death records. Its just a matter of if you want to go through the process and expense of having a supplemental record made. If you wish to pursue it, you probably should start with contacting your state dept of vital statistics/records.
To my mind the best way is to make the corrections here on Wikitree and add a dialog or research notes explaining the discrepancies for future researchers. Also, where possible make comments or corrections on any other websites that come up with the incorrect record. That is how I have dealt with such things.
Just my two cents and I hope this is of some help.