I think a crime of passion would be killing the man (or woman) if you walk in on them in bed. Killing someone raping a child would be a self defense. (especially if she felt she was protecting the child’s life... by saying “I thought he was smothering/choking her”). Either way.. put me in the jury. Not Guilty.
It can be proven that the loss of "soundness" was the result of her observing her child in danger, and that her anger overcame her reason. Since she recovered her reason once the rage had passed, it was only temporary.
Thus, a defense of temporary insanity.
"Insanity" has a very precise legal meaning; it does NOT mean "crazy."