Who hammered a spike into Teramalda, and why?

In 821, Garmar Four-Beard captured Teramalda, and having failed to strip her of her armour, decided to bake her alive. That went badly, and to this day the undead Teramalda and her armour roam Ravenland. The only way to kill her is to remove the magical iron spike driven through her chest (which requires a FORMIDABLE MIGHT roll, which is less impressive than it sounds, as modifications don’t affect base dice, so your combat character will still be rolling 4+ dice).

Where did the magical iron spike come from?

It can’t be from Garmar. He wanted her humiliated, or, failing that, dead; dead in a different way that left her armour mostly intact isn’t something he’d have wanted.

It can’t be from the Rust brothers later on: Teramalda needed to be undead before they decided that she was the poster child of “mess with the Rust brothers and undead are gonna get you”.

Also, why could Teramalda’s armour not be opened? Armour is designed to resist bad guys with swords, but not armour-wearers who would like a rest now that the fight is over, and not have to cart around many kilos of plate mail. If you’ve subdued someone wearing armour, you can find the buckles and catches that let you remove armour pieces bit by bit.

So I think what happened is that someone found a wounded (possibly dying) Teramalda on the battlefield of the First Alder War, and they made a pact that by driving a magical spike into her heart as she was dying, she would come back to unlife instead, driven by a desire to kill basically anyone. Garmar was merely unlucky, as he didn’t recognise that the “living human” he decided to roast alive was in fact an animatronic already planning to kill him.

So: who drove a magical spike into Teramalda?