Not just yet. The overhead glacier is not considered a reasonable avenue of approach.

Still, this will complicate their approach. 

What does Brigid know of the guardians? 

"...Those are new."

"Have you seen their like before?"

"No. It looks like he reanimated some dragons."

"Are they likely as powerful as living dragons?"

"Probably not? Most things don't- make the transition gracefully."

Hmmm... She'll ask a few more questions about vulnerabilities, powers (after making sure they're unlikely to be spotted) - would, for instance, shooting them with a non-magic siege weapon work? 

Undead are more resilient to damage than mortals- they don't feel pain- but if you can blast them apart, that should do the trick.

She can do explosives, and she can do cannons, and she can do fireworks with an explosive payload - unfortunately for this circumstance, no one's managed to combine cannons, high explosives, and general anti-personnel weapons yet. (Probably fortunately for her planet, though.)

Siege weaponry would be more appropriate for dragons.

So cannons it is?

So it would seem.

She'll need a defensible place to fire from, one with good sight lines - though the dragons are being very helpful by not moving much. 

Ling and Brigid will have to be cautious about their own movements, this close to the citadel.

Avoid drawing attention. 

They don't have a lot of other advantages up here.

No - but it's a big one. 

Yeah.

What does she need Brigid to do?

Play lookout - Ling needs to know if she's at risk of being discovered. 

She can do that.

Then what remains is - slowly, carefully, sneakily - setting up the most powerful weapons she knows how to make, their ignitions attached to alkahestric arrays, several trained on each dragon, and a few more trained on the castle itself and just at the general area in case the dragons startle - she mixes explosive fireworks into that - hopefully enough for a rapid barrage to wipe out most resistance before they can take cover. 

She manages to do this apparently without anyone being alerted.

Then, with her and Brigid firmly under cover: 

Fire.

More like ice, really, because of the ensuing avalanche haha get it?

The damage is, ah, considerable.