I think Malekith would probably kill her- he's got WS8 (or 9? Think it's 8) compared to Mathilde's 5 in there, though Branulhune is much more broken at disabling Magic items than Destroyer is.
Yeah, even in ideal circumstances (solo fight, and maybe even an ambush), it's more likely that he would win than her.
Malekith's kitted out to be extremely anti-wizard - his
The Destroyer randomly destroys a magic item on the person it hits, his
Supreme Spellshield gives him Magic Resistance (2) and deals D6 Strength hits to anyone whose spells he manages to dispel, and his
Circlet of Iron makes it easier for him to cast or dispel spells. And if this wasn't enough, the
Armour of Midnight has a +5 armor save and a
+2 ward save against non-magical attacks (a massive protection against mundane attacks).
So Malekith is essentially only really vulnerable to magical attacks that aren't spells. The thing that thus makes the fight winnable for Mathilde is Branulhune. It's a gamble, really: A gamble to see who can hit who first.
If she's lucky and gets a good hit it, then cheers and celebrations, that means all the above-mentioned magical items he has are dispelled. And thus Mathilde 'only' needs to defeat a millennia-old master swordsman who is also a master user of Dhar. But he's on the backfoot, and she still has the Belt to cancel out at least one spell. That shifts the odds significantly in Mathilde's favor.
If she's unlucky, then she gets hit with Destroyer and it, well, destroys one random magic item she has. Elves are incredibly fast and it wouldn't be surprising if he got the first hit in. Mathilde has ten magic items on, but I don't know if the Coin, being a divine artifact, is capable of being destroyed by his sword. So let's say pessimistically that there's a 1/9 chance that Branulhune is destroyed and that essentially makes the fight completely unwinnable. Or she could lose her Seed of Regrowth, or her Belt, or her Robes, all of which could make all the difference in the fight. In the best case scenario for this she loses her Candle of Cleansing Radiance, her Dragonflask, or her runed revolvers. But that's still a net loss.
...And Malekith, of course, is not typically the sort of dude to be met in a white room scenario. He has a dragon, he has armies, he has other hero units with him. Unless we specifically ambush him when he's about to take a bath or something, at least a few of those will show up and shift the already-terrible odds in his favor.
I'll remove the specific reference and leave the Magic Item/Divine Item distinction as an exercise for the reader. Thanks for the input!
