I adore Mavis, too! I think that would be a nice, subtle way to honor your yiayia.
I also just thought of using the meaning of Stella ("star"), since that's the name she prefers. Astra, Astrid and Esther are possibilities there. :)
If you're tryingGreek, maybe Thalia, or if it's a boy Perseus(Percy) Percy could also make a cute and surprising name for a girl. Good luck!
My first thought it Peris/Paris or Arista
My favorite bird name is Adaryn/Aderyn or just Deryn, Avis, and Lark
I think you could use Peridot to honor the name Peristera. I also think Maris would honor her because of the term Stella Maris. I also really like the idea of using Paloma. Good luck!
Since Stella means star, what about:
Estera - a Polish variation of Esther, but resembles your yiayia's name so much that I think it could be a real contender
Roxanne / Roxana
Seren - another good name in my opinion
Tera / Terra