[Spoilers] The big hint at the end of the "Return to Lordaeron" questline

She totally does. She was send by Anduin to undermine the Horde war efforts. Literally her first action on the council is to trying to make Forsaken forces get out of Gilneas. A place that has been rightfully conquered by the Horde during the last war. Because ALL of Lordaeron belongs to the Forsaken. She is an alliance spy. That much is obvious.