mcv, reread the section on Astral Intersections (p. 316) again. A spell, would qualify as an astral form which is bound to a physical object (the spell is tied to the person it is cast upon). When the person passes through a barrier it causes an astral intersection and the two would make an opposed test.
I f this is the case, I'm surprised that the rules don't state this explicitly. A person with a spell cast on them walking through a mana barrier seems like the most obvious case. The fact that the rules resort to elevators and vans to explain this, suggests strongly that this rule is not meant for the simple case of a person walking through. If it was, why not simply say so? The section sounds like it's dealing with exceptions and edge cases, rather than the simple most common case.
If the spell fails the test, then it is disrupted and ends. That's why spells are listed in the list of things that can be disrupted.
Dual-natured creatures have an astral form, so they are subject to the same limitations as other astral forms, so they can't walk through a ward without being subject to an astral intersection.
So what happens when a dual natured creature is disrupted? Do they stop being dual natured? The rules also say that if the ability is inherent, like with Adept powers, the mana barrier doesn't stop you.
Maybe if it's just astral perception that makes you dual natured, the astral perception stops working but can be reactivated once you're through? That makes astral perception a cheap way to try to destroy a mana barrier. Unless your astral perception is inherent, in which case it doesn't disrupt the barrier.
Pushing through a barrier is available to any awakened creature, but it takes an action, so they wouldn't be able to do it without warning. If you are trying to move any active magical effect through a ward, you would need to push through.
So basically the options are: you push through carefully, or you take a 50/50 chance of destroying the barrier, or you can cast a spell from outside to inside with a chance it gets resisted.
In our case, the spell was Invisibility. The street sam got Invisibility cast on her and went inside. The mage was already bummed by the barrier, but if the spell had destroyed the barrier for him, I bet he'd have been pretty happy. He could also have cast a spell through the barrier on the street sam once he was inside, and as long as it's not a normally resisted spell (which most buffs are not), then there's a pretty good chance the spell will be successful.
All in all, using the intersection rules for a spell passing through the barrier seems rather dramatic and makes the barrier very vulnerable.
In any case, this seems like a very badly written rule. It would have been very simple to treat spells more explicitly than letting us deduce it from astral patterns and examples with vans.