The weights are pretty much the crux of my argument, another debilitating factor is that the shield is also exceedingly heavy, (it should definitely be heavier than 15 pounds that you state, but 15 pounds is still weighty.) so gravity would actually be against you in trying to stop the downwards momentum of the sword strike.

I'm happy to accept that either she suffers some form of fracture (weakening the wrist/arm) or the blade cuts through the armour but only enough to cause a pretty painful bleeding wound, not enough to completely disable the forearm/wrist but enough that the damage is felt.

I'll happily accept some burning, though I don't believe the blade could be moved fast enough to cut because of the pivot coupled with the burning factor it may make it through the tough leather of the boot to burn the skin (I've watched some videos on test cuts, you'd be surprised the difference something as seemingly weak as cloth makes on a cut, tough leather would probably be ample protection if the blade wasn't magic) though it would only be a surface wound IMO and not nearly as debilitating as the longsword strike.

Also, for an object like Hyperion, 15 pounds would still be a serious amount of weight. An ordinary spear is what, around 2-3kg at most? If you're looking at three times the weight of a wooden spear roughly that would be an exceedingly difficult weapon to swing. 

Dunno, is that a fair trade-off? Pollen, Chimera?