Has it occurred to you that perhaps...
The mother was a shapeshifter of some description?
I imagine that you may have killed a wolf in order to sustain or defend yourself, without realising it was this- rival's mother...
This is on the assumption that your rival isn't under a delusion of some kind.
1.5 imperial gallons of tea were consumed during the writing of this postAhh... the word typically.
-smiles slightly to himself as if amused-
Always the chance of flukes- -his face returns to a more serious one- or as you say, ones rendered into a form permanently...
Certainly if this were the case- then you had no way of knowing that it was this rival's mother.
It'd certainly be a matter to be debated in court... probably manslaughter rather than murder.
1.5 imperial gallons of tea were consumed during the writing of this post"Even then, the likelyhood that any animal I hunted could've been her before she perished from a mess off things- and even then! There would be no way of finding out!"
"On a nation-wide scale, she's stowing away secrets that are directly causing the fall of this very country. More personally, she murderered my mother."
-he adjusts his hat with a sigh, leaning back in his chair-
Ramona, that will just agitate her and make her more committed to pursuing this justice she seeks.
You will be giving her more reasons to hate you.
More reasons to want to kill you, potentially.
Do you want that?
1.5 imperial gallons of tea were consumed during the writing of this post

Because it doesn't have much footing as an actual holiday?