The preaching part is also done by Mormons, certain Evangelical Christians among a number of groups...you might ask her if D2D is the only true form of preaching. What about the numerous religions that use mass media to spread the word...or missionaries doing medical or humanitarian work while spreading the Gospel? D2D is just one way to preach...and a rather ineffective one at that these days.
As to going to war, there are many religions that refuse military service...Quakers, Mennonites, Seventh Day Adventists, Christadelphians and Unitarian Universalists come to mind immediately. The "refusing to go to war" claim is one of the weaker arguments for the "rightness" of the WTS.
It sounds like she is starting to see TTATT, so be patient and help her come to her own conclusions...good luck!