I think she does it deliberately, and I think she does it to put certain people on notice. Her rejection of the budget was probably carefully orchestrated. Look at what she said about a year ago when she rejected it : "I am here today to fulfill my responsibility. To do otherwise would violate my constitutional duty, and that I will never do."
She's also tossing flames around in the media over Perry and others trying to have her responsibilities moved over to the legislature or govenor's office, kind of a "Rick Perry wants to have the fox guarding the hen house and I'm not going to stand quietly by" strategy. This would play well in 2006.
Perry should not have crossed her over those responsibilities, for several reasons, the least of which he could find himself running against her or Senator Hutchison. He'll find that all those things he did for Tom DeLay won't help him out - DeLay will stay far far away from that struggle, because he values his job too much.