KT may have not done it on a whim, but she still wrote a very poor death scene. Outside of her Commando novels, Traviss was not a very good SW author. She even did a poor job writing Jaina Solo in the Revelation novel. I am fine with Mara being dead. I am not fine with the way her death was handled. Mara deserved a more epic death. Zahn should have been consultated, as well. His input would have been very important considering Mara Jade was his character. KT is not just the "fall guy" for a unpopular decision. Her decision is hated because of how poorly it was handled.
She didn't act unilaterally. I've read extensively on the writing process for the recent multi-author series and it's a team effort. Zahn was not on the team. In addition to initial outlines for the whole series designed by the whole writing team, there are ongoing discussions amongst them as well as editorial and content oversite by both Del Ray and Lucas Arts.
What Travvis has become is the "fall guy" for an unpopular decision. I'm sure RA Salvatore is glad she's come along to become the new whipping person. But by no means did they just get to kill characters on a whim.