* Όμορφη γιαγιά (Omórfi yayá): This is the most straightforward translation. "Όμορφη" (omórfi) means beautiful, and "γιαγιά" (yayá) means grandma. It's simple, clear, and widely understood.
* Γλυκιά γιαγιά (Glykiá yayá): This translates to "sweet grandma." While not directly saying "beautiful," "sweet" often implies a gentle beauty and is a very endearing term.
* Εξαιρετική γιαγιά (Exairetikí yayá): This means "excellent grandma" or "wonderful grandma." This option focuses more on the overall positive qualities of the grandma, hinting at beauty through her excellence.
The best choice will depend on the context. For a casual conversation, Όμορφη γιαγιά (Omórfi yayá) is perfectly fine. If you want to emphasize kindness and charm, Γλυκιά γιαγιά (Glykiá yayá) might be better. Εξαιρετική γιαγιά (Exairetikí yayá) works well if you want to praise her overall character.