she is a well-written character in that sense and that her role in wot is important. i think getting her into power is the whole reason for the white tower split too - keeping siuan alive was obviously meant to have a good teacher who just went through the amyrlin rigmarole (as opposed to egwene having to learn all the bs by herself). if the tower was whole (and if siuan had died), egwene would never have become amyrlin. we have to assume that this is her purpose, whether or not she is a good person