Izabela Lubomirska's Wikipedia article is here. She was born into the Czartoryski family and married Stanisław Lubomirski. Google's translation of Marquise Lubomirska's Polish Wikipedia article states she wore blue skirts, as shown, so she was called the "Blue Marquise."
This is Isabella Lubomirska, née Czartoryska, not Izabela Czartoryska, née Fleming.
