Who Is the “Little Sister” of a Medieval Rosh Hashanah Prayer?

The little sister says her prayers
And performs all her devotions.
May’st Thou, Lord, her ailments mend.
Let the year and its ills end.

אחות קטנה תפילותיה
.עורכה ועונה תהילותיה
,אל נא רפא למחלותיה
.תכלה שנה וקללותיה

So—no doubt puzzlingly to many—starts the well-known piyyut or liturgical poem that is commonly sung or recited in synagogues before the evening prayer that ushers in Rosh Hashanah. The piyyut has nine stanzas, the first eight of which have the identical refrain while the ninth contrasts with them, thus: