Antoninus Pius, Alexandria? Silver Coin, Found Egypt. What Is The Reverse Image?

I'm pretty sure this is the portrait of Antoninus Pius as it matches one of his. A more precise ID would be a help.
Ditto the obv legend (AVTKTA is all I can read) which would appear to be part of AVTKTAIAΔΔAΔP ANTWNINOC CEBEVC which similarly appears on an AP Alexandrian coin. I was mystified at first because I didn't think there was a V in Greek (it's not in the CC Greek character list).
Who is in the reverse image? It is very distinctive and I can't find another anywhere. Alexandria herself? And what is over her shoulder.
Are those date letters beside her?
I'm afraid I don't have size or weight. It belongs to a friend whose grandfather picked it up in Egypt. From memory, the silver flan is thick and about 15mm diam. That's all I know.