In the English language there's the option to say my paternal grandmother, but does such a convention work further back? For instance my paternal maternal great-grandmother?
When the family becomes that extended, it no longer is appropriate to be so specific. (Formally)
If your conversation requires this level of specificity, you would clarify it with reference to the entire line if necessary. Otherwise, "Distant Grandmother", or "Ancient Grandmother" covers all grandmothers more distant than "Great Grandmother"
A general rule, is that if you couldn't have met her, she doesn't have a specific title in relationship to you. Even the royals referenced these relationships as commoners would. After the 4th generation, they would use the official title, rather than the filial title.