Theory about a Name

In Cold Days after Harry summons Mother Winter/gets dragged to the cottage, Mother Summer asked about what names Harry used, and then asked if he used a name they share.

Could the name they share be Themis.

We know that the Queens of Summer and Winter collectively make Hecate. It stands to reason that the Mothers name would come from the same mythology.

Themis is one of the Titans, above even the Greek gods. She represents not only justice, as he usual depiction holding scales of justice indicates, but also represents the seasons and balance. The Mothers are nothing if not in perfect balance with each other and would tie into Hecate/Fae being tied to the seasons.