Spanish Noblewoman. Pretty sure she's Catherine Hapsburg as I suspected last chapter then.
Her staying in Arte's house is a nice twist though. This arc more than any other feels like it's building on everything before it: Artes' becoming known as a portrait painter and decision to stay as one, her acceptance of her unique status as a female painter and change as seeing it as a strength rather than weakness (from the Venice arc), even the more mundane things like wearing the clothes Yuri gave her and coming back to her childhood home. Even if this was more of a setup chapter than anything else I expect great things from this arc.