Grandmother (also Grandma, Grandmama and Princess) of would-be Storm Kings. She rides herd on Houses Sturmvoraus and von Blitzengaard (not to mention the Storm King Conspiracy) and is also the superior of the whole order of the Smoke Knights, or at least Violetta's branch of that organization. As Violetta claims cousinhood with Tarvek Sturmvoraus, it may be inferred prior to proof that "Grandma" is the senior member of the cadet branch of Valois (or possibly Sturmvoraus), which would make her the likely Commander General as well.
When her relatives speak of her, they invariably refer to her as just "Grandmother," usually in tones of fear and respect,  while in Paris she is referred to as Highness by her servants and ' ' by Mister Obsidian. It finally takes the Master of Paris himself to that her first name is Terebithia.
She apparently makes the major decisions for the house(s), or at least to make the ones that stick, especially now that post-Timeskip she is reported to have lost her and has become/taken over the duties of The Council.
Of course, there's the (increasingly unlikely) possibility it's a codename, like "Mother".
Her ability to throw a party has also achieved her a degree of infamy; it was her Agatha commandeered for her escape from The Refuge of Storms. And after hearing numerous passing mentions of her, the reader finally in person in Paris talking to Seffie on that very subject, as Agatha and Tweedle's arrival sends social (and potentially physical) shockwaves through the city.that
Lucrezia, and has ordered all of her followers to break off contact with the latter woman and her forces. Smoke Knight cells still loyal to Lucrezia, like one led by Madwa Korel, have been burned from the cabal, and all other factions' smoke knights have standing orders from Grandmother to set aside rivalries and cross agendas to pursue the rogue cells for elimination should they be encountered.to Violetta at least, Grandmother hates
Possibly Relevant Information Edit
Grandmother's given name is presumably a homage to the 1977 children's novel Bridge to Terabithia by Katherine Paterson. (Note alternate spelling.)