In the context of insurance, one speaks of "fault", rather than "mistake" in this context. In fact, it seems from the Asker's later discussion entry that the victim was a man. A couple of people seem to have imagined it was a woman, having failed to appreciate the fact that, in French, after the feminine "victime" related pronouns and nouns will also take the feminine form, even if the victim was a man. However, if the sex of the victim was unknown I think that nowadays the acceptable way of dealing with this is by using "they" as a gender-neutral pronoun.

I think that SafeTex is completely wrong in his interpretation that " the writer wants to suggest that she is wholly at fault for the second "event". On the contrary:

" l'on ne peut lui reprocher sa propre faute à l'exception de sa faute inexcusable, qui se définit comme une faute volontaire, d'une exceptionnelle gravité, exposant sans raison valable son auteur à un danger dont il aurait dû avoir conscience."

In spite of the missing "pas", it is clear from how the sentence continues " à l'exception de sa faute inexcusable …", that the writer is saying that the victim cannot be blamed for his own fault unless the fault is inexcusable because being deliberate, exceptionally serious etc. This extract actually does not go on to say whether or not those circumstances applied. Presumably, your text does go on to make a statement about that.

An example of a fault to which those exceptions applied would be that of a pedestrian who suddenly stepped into the road without looking (but with no suicidal intention), when an oncoming car was too close for the driver to be able to stop in time to avoid hitting them. In that case, the pedestrian would have been responsible for "une faute volontaire, d'une exceptionnelle gravité, exposant sans raison valable son auteur à un danger dont il aurait dû avoir conscience."