The speech patterns don't match Venli, Taravangian, Malata or Sja-Anat, and as Navani said, which fabrial? None of the ones she uses capture sapient spren. On the Sea of Lost Lights map though, one of the notes says spren fishing is illegal there, which makes me think not all spren think the same regarding their non-sapient brethren. Iri joined Odium, I think some of the spren probably did the same as well and the speech patterns made me think of spren.