Drogo's death meant her death. There is absolutely NO indication that ANYWHERE in the book that she meant to kill Drogo. It is clear that she tried to save him. If you can't see that, then you're just bad at reading.
Except the whole dialog about her already being raped, her family and friends slaughtered, village plundered and her saving other villages from the same fate. I guess she didn't mind if it was only the local villages that Drogo was going to personally destroy but once some old crones declares an unborn baby to be the stallion that mounts the world, that is where she draws the line. But maybe there was a chapter with her as POV and explained everything that I missed?