Spoilers, highlight: In the mass pregnancy mission, the Aviator doesn't appear to have been affected by the potion, since she didn't pass out along with the others. (The Aviator flicked a few colored droplets off her robes in annoyance, though the annoyance soon turned to amusement when one by one, everyone who had been doused began to pass out.) So it doesn't quite make sense for her to have become pregnant.

For one think, I've read on the wiki that Eragon's a Canon Stu, so, maybe, if it deflects stuff like swords and arrows. It should probably deflect bows, too, but I don't think anyone's going to try to kill him with one of those directly.

They probably think that the puny bullet wouldn't dare to hurt their Great and Mighty Sueness. I wonder if Mary Sues ever get the phrase "Killed by Personification" engraved upon their headstones.