Jestina wrote...
From what I recall from DA:O the mirrors were a communication device, used by a kingdom of elves that no longer exists. Now the remaining ones are used as portals, usually by demons and darkspawn.
The one she's repairing probably leads to a lair of darkspawn or something...which is why Duncun destroyed the thing.
The problems I had with Merrills character in DA2 was that they made her overly naive and weak willed. For an elf messing around with blood magic, she sure didn't last long in the fade when it came to resisting temptation from a demon.
She had so much potential from DA:O too. I was disappointed with what they did to her in DA2.
Several things:
As I understand, there are only 2 remaining Eluvians: The one that was broken and that Merrill repaired, and the one that Morrigan used. There is no evidence (that I'm aware of) that says that they're used by demons/darkspawn as "portals". The reason Merrill's mirror was taint-infected was simply because darkspawn were in the vicinity (IE the temple). I'll give you that it probably leads to the Deep Roads (IE the ancient thaig), but who says eluvians have set locations?
Duncan likely destroyed it simply because it was taint-infected, had already lured and killed one Dalish Hunter and corrupted another. Not necessarily because it led into the Deep Roads, although that is a possibility.
Also, the Fade quest is very silly to me on multiple levels. In-character, the fact the whole thing was taking place in the mind of a Somniari created rather unique conditions, as it seems EVERYONE (except Justice and Hawke) had their willpower scores set to zero there. Even in DAO, the only reason people fell for demonic deception is because to them, it was seriously like being in a dream, with a corresponding lack of rational thought.
OOC, it was simply a) a hamhanded attempt to show how awesomely uncorruptible Hawke is, and

a reminder that your companions have their own desires and agendas, and may place them over Hawke in the future, foreshadowing the ending a bit.
Finally, people always say that Merrill is weak-willed and easy to give in to temptation. If the Fade is your evidence there, in that case EVERYONE is weak-willed. Aveline, Fenris, Varric, and so on all gave in as well (Anders cheated). If it's simply because she worked with a demon, that's because she decided that simply put, the risks of her getting possessed or dying were worth the potential benefit of getting an eluvian to work. She didn't go into it assuming everything would be fine. She thought about it and planned accordingly..