I'm going with the 'clever' plan. This is somewhat magic heavy (depending on how long it stretches out), so if it's too much of a strain on her to keep this up, let me know. This also got rather long, so let me know if you need it compressed. The overall plan is quite simple, but a lot of the details are added to actually make it believably workable.
[x] Time to play.
-[x] The tunnels are already a maze, but a maze can be figured out if it never changes. Who said it never changed? Use illusion magic to seal off or open various parts of the dungeon to give this party a guided tour that will never end.
-[x] Illusions only go so far, especially since our dungeon isn't that large yet. Have goblins follow after the adventurers and mask or rewrite any marks they make to help them find their way through the dungeon. Also do things like clean up or add trash to various hallways, so that the same tunnel never looks the same twice.
-[x] Have the goblins occasionally harass them, but never fully engage. Giggling from the shadows should have a nice "rats in the walls" paranoia effect.
[x] In the meantime, have Aruna set up something at an ambush spot (possibly near the entrance, since we'll have been keeping them away from there) that we want to herd the party into.
[x] We want them very worn out before that point, though. A long, tiresome, fruitless tromp through the dungeons should have them on edge and bickering with each other.
[x] Eventually lead them to the trolls. Have goblins on the sides helping support the trolls' fight.
-[x] Lend your own support with a Frost spell from the shadows. Only use Fireball if you can ensure it won't hit the trolls, and won't kill anyone from a direct hit. Maybe as a final spook to get them to run.
-[x] At this point, the group should be feeling somewhat overwhelmed, and at least the thief or the mage should attempt to retreat.
[x] The escape route from the trolls should lead straight to Aruna's trap. Prisoners ahoy!
