Why, if she was seized in an illegal US raid in Syria? Why was she not handed over to the Syrian authorities for trial on whatever happened in Raqqa? On what grounds was she detained by foreign fighters illegally on Syrian soil in the first place? It is also an expression of the recognition of the independent Kurdish state by the US. State Department? Note the way this is dressed-up.
Abu Sayyaf was killed in a Delta Force raid of his Syrian compound in June, which resulted in a treasure trove of intelligence about the Islamic State group. Umm Sayyaf has been turned over to the Iraqi Kurds for trial.
UPDATE 9th Feb 2016
A 25-year-old Iraqi woman. Nisreen Assad Ibrahim Bahar, also known as Umm Sayyaf, the widow of the slain ISIS leader was accused this week of taking part in the 2013 abduction of Kayla Jean Mueller.
The Justice Department said she is in Iraqi custody for terrorism-related activities. "We fully support the Iraqi prosecution of Sayyaf and will continue to work with the authorities there to pursue our shared goal of holding Sayyaf accountable for her crimes," said John Carlin, assistant attorney general in charge of the Justice Department's National Security Division. "We will continue to pursue justice for Kayla and for all American victims of terrorism," he said. Prosecutors said Umm Sayyaf threatened Mueller and two other women who were being held, "telling them she would kill them if they did not listen to her."