Disarming someone by hitting the end of their sword is actually pretty difficult, you have to hit pretty hard and fast at the end near the hand otherwise the sword just flexes and absorbs the momentum, which is what I said would probably happen. To answer your question, a shield is not armour, armour is armour. My posts tend to be vague on -certain- issues because I'm posting from my character's perspective, who unlike yours does not have superhuman observation. Noticing what the spear off to his left is doing or the tip of a gladius sticking out of a shield are not things that are easy to do in a split second confrontation, at least for an ordinary human. 

Also, your attacks are anything but simple. You still never really clarified exactly how Iolanthe was holding the shield out towards Sigurd in the first place, but presumebly unless she was holding the shield out straight when she dropped it with the consequence of leaving herself completely open, I'd assume she'd return to an ordinary shield on arm holding position (upper arm vertical, lower arm horizontal) which would consequently reduce her overall range (unless she had extraordinarily long arms) to about one and a half feet as the shield dropped down. The longsword is three feet long, so in my estimation it would not hit the sword close to Sigurd. This is just my evaluation of the move, I can't know for sure because certain key details were emitted, which in my defence means I can interpret it however the hell I want. 

Sigurd's sword -may- have hit the gladius on the way across if she managed to move the shield into position. However, that wouldn't do very much as I mentioned the tip of a sword has a lot of give. It would just flex and the heavier longsword with actual rightward momentum would slap into its side, her hand would twist slightly and the longsword would keep going. However, I don't really know for certain how it would happen, so I just accepted the end result would be the same, Sigurd's sword off to the right. He's not been able to immediately attack with it, so by extension I'd say your plan was still semi-successful, he's had to manoeuvre it back into position for a turn. 

Finally with the spear I assumed Sigurd's sudden dash forward would put him within its effective range, so the edge would be against a new part of his leg but would have to begin the burning process again. Sigurd's armour is pretty poorly described, though I would never have it outright block a blow like your character's has done twice now, so it doesn't really matter much. I could try and give a more detailed description, but predominantly there's iron plates on vital spots, aka chest, shins and groin. Everything else is fur and leather.