"Hello my maternal grandmother"
So even with a Navajo keyboard app...which btw was a pain to find-it will NOT give me a "correct" for this phrase...even using the preset from the app!!! This one- Yá’át’ééh Shimásání!
Yáʼátʼééh! I think that it will depend on the kind of keyboard. For example, I use Multiling Keyboard to use the Navajo layout, and the writing is correct on Duolingo. But, it seems the Gboard (Google keyboard) uses a different apostrophe (I think this is the closing smart quotation mark ’ ), and Duolingo uses ʼ.
Note: I really do not know how the other apps are working with Navajo for different platforms.
Edit: here is another explanation in the forum.