I really liked this -- so clever and layered and well-written. Thea is an excellent OC, and I love seeing Rita's vulnerability and complexity. You've made both of them very real. I love Rita fic in general, especially when she's presented as well as she is here, flaws and all yet very appealing despite them; she's quite believable. And I can see why she'd be attracted to Thea, who represents just the sort of beautiful, powerful danger that Rita would find compelling.
I love Rita's opportunities with "interesting women," and of course, my Minerva/Wilhelmina-loving heart just adored the hint of that pairing (which was the basis of the first HP fic I ever wrote). Love how Amelia and Wilhelmina return for mentions later, too; such details do a fine job of adding texture to the world of the story.
So many great lines that I know I'm going to miss some:
They lie together in bed, blankets tangled about their feet, conversation and heavy breathing muffled by the Silencing Charms that serve as their only cover Such a great opening overall.
Slytherins who do not learn when to conceal their rattles are soon deprived of their fangs. And Rita is determined to make the most of her own natural gifts Your Rita is so perfectly Slytherin, in such good and bad ways.
Rita is a creature of the present, moving onward and upward, never stopping to look back in case something catches her. Just exactly how Rita would see herself, and I like the way you show us that it's not quite an accurate assessment.
Blaise, Thea explains, is in England with his grandmother, saving Rita from some deeply awkward sentence constructions. Haha!
She puts the odds of either running straight back to England or falling into Thea’s arms at even. Ah, I love your Rita. She actually does know herself pretty well.