Is Grandma telling you information about events that took place when she was a child? Sometimes children get things correct and sometimes they don’t. This situation can be aggravated if the adults don’t really tell the child anything and the child only hears a few details. Sometimes they, without any ill intent, create details to fit what they hear, or they interpret things through a child’s eyes, which may not entirely be correct.
If you have children of your own, think about how they misunderstood something once in a while. Then remember: Grandma was a child once, too!