Mirror of Distance
The Mirror contains the Summoning the Distant Image -effect (InIm25, R:Arc, D:Conc, T:Room), done with Faerie Magic (which lowers the level from 25 to 20).
What does it do? Here's a quote from Ars Magica 4th Edition:
You can see and hear what is happening in a distant place if you have some
sort of arcane connection to either the location or a person there. If your
viewing area is outside, you can only see and hear for a distance of about
five paces. Outside that range the images and sounds get hazy.
Mirror is a good item to put this kind of effect in, since it gives both +3 Scrying and +5 Imaginem Form and Effect bonuses. Combined with the new True Illusionist -virtue and Faerie Magic, Nelly is particularly good at this kind of magic.
The mirror is made as a lesser enchanted device by Nelly. Her Intellego Imaginem lab total is 48, leaving 4 points for effect modifications. They are used giving the item 12 uses per day (+4 to effective level). It is still possible to create the mirror in one season as a lesser enchanted device.
Since the item is made with Faerie Magic, some of it has drifted into the original spell effect. When scrying through the mirror, ordinary people pick up some faerie-like traits, and faeries some humanlike traits.