Top five reasons why Hebichi should never have her position swapped with Sasuke.

1: Itachi would be turned into shish-kebob, or more likely she would force him to tell her why he was going to kill their clan.

2: Danzo would get his ass kicked by the both of them. Hebichi could just use her kekkei genkai to kill him in his sleep.

3: Itachi would have been forced to spend more time with her, by the attention-craving child herself, and it's likely he would have had a slightly different view on the world that might let him think of another solution.

4: Hebichi wouldn't have been as clueless to what was going on in the village. She could inform Itachi beforehand, and he could tell the hokage.

5: Danzo is annoying and like my father. So I would have killed him off before the fanfic even started :)