Atris is, in a word, dumb.
Her life is defined by your life, as the player, and most specifically by your actions in the face of her own inaction. She feels perpetually inadequate for not following you to war, partly because she idolizes you and partly because she feels that her failure to fight was a sign of weakness on her part. Everything she's done since your exile has been warped through this twisted lens of an inferiority complex, with a wonderful dash of love/hate for you thrown in.
This inferiority is what led her to first begin to consult the Sith Holocrons she has for knowledge; she believed that she could use them to learn more about the Sith that were hunting the Jedi, and in so doing to overcome what was threatening to be another period of inaction and failure on her part. But the Holocrons manipulated her and twisted her feelings of inadequacy and weakness until Atris came to hate everything that wasn't her, including the Jedi themselves. This is why she leaked the Jedi Conclave on Katarr--she did not view the Jedi there as real Jedi any longer, and so thought their sacrifice would be an acceptable risk in return for drawing her enemies out. Her total failure to actually engage those enemies, plus the death of the entire planet (not to mention the Jedi), only forced her to plunge more deeply into her web of self-told lies in order to avoid putting the blame upon herself.
Eventually the only tool she could spend that didn't necessitate her own involvement was you, and so she did. Rather than risk herself, Atris, feigning action, instead risked the last piece she had left to risk, her hated hero. But this brought Kreia to her, and eventually the revelation that her feigned adherence to the Jedi was entirely a fallacy. When the Exile finally reaches Atris for the second time, then, Atris is determined to kill them and finally begin moving forward--though whether or not she actually would have is incredibly suspect.
The thing is, Atris is weak and is indecisive, as well as pathetic and cowardly. She represents the absolute worst of the Jedi, worse even than the rest of the Masters, because she is the only one of them that not only refuses to adhere to the code, but actively breaks it and harms others, all in the name of casting blame away from herself for her inaction. She does the most harm while doing absolutely no good, hidden away not only from the galaxy at large but also from her own creeping inferiority complex. Nothing of what she does is logical, and all of it is the result of a mountain of lies she has constructed in the name of justifying her isolation, and the sacrifice of everything she was meant to protect for--so it turns out--nothing.