I think you forgot something really important: when a new PC comes onto the scene, she is blurry and blinky for about ten seconds; during this time, she is invulnerable.
Oh wait -- that's Super Mario Brothers I'm thinking about. Wrong game.
Actually, I think it's a good idea, though, and one I've used in a similar situation (in a new PC's first combat, a demon suggested that she attack the party barbarian; she did so, and the barbarian attacked back, and criticaled, killing her in one blow). If a PC is about to die ignomiously (sp?) before she gets a chance to do much of anything, consider stretching the rules a little bit.
In my case, I had her stabilize at -9 HP and lose a point of strength for every HP beyond -9 that she would've lost otherwise. It knocked her completely out of this combat, but she was able to enter into affairs later on.
In the future, you may want to consider something similar: give a new PC immunity from really unlucky dice for her first session. Stupidity may still get her killed, but she won't die because of luck.
Daniel