So balefire can burn back just a few seconds, or a longer period. When Rahvin was killed, Rand burned him back a good hour or two (if I remember correctly), and he must have burned Graendal back pretty far, depending on how long it took her to throw the Compulsion on the mark and send him back to Rand. But if he only burned Semirhage back a second or two, then she would still have made him strangle Min.