Just to streamline the math (I always find [Te]Vim guidelines quite confuse): "Dispel effects of a specific type with a level less than or equal to the level + 4 magnitudes of the Vim spell + a stress die (no botch)."
- A lvl 1 spell with R:Personal, D:Momentary, T:Individual would dispel an effect up to lvl 5+stress die (Base 1 +4 mag = 5);
- A lvl 2 spell with R:Personal, D:Momentary, T:Individual would dispel an effect up to lvl 10+stress die (Base 2 +4 mag = 10);
- "Erase the Mirror" must dispel at least a lvl 10 effect for sure (meaning the base must be 2), but the Range must be Touch; therefore, "Erase the Mirror" is a level 3 spell (Base 2 +1 Touch) that dispels a lvl 10+stress effect (Base 2 + 4 Mag).
A magic item that casts "Erase the Mirror" up to 50 times/day would have an enchantment lvl 9 (lvl 3 spell + 6); to be more cost effective in vis terms, it could go up to 10. Then, it could be useful to raise the spell to lvl 4, with two options:
- base 3 +1 Touch, effect base 3+4 mag-> dispel lvl 15+stress, no penetration);
- base 2 +2 Voice, effect base 2+4 mag-> dispel lvl 10+stress, no penetration).
Another options would be lvl 5, with only 24 uses/day:
- base 4+1Touch, dispel base 4 +4 mag -> lvl20+stress
- base 3+2 Voice, dispel base 3 +4 mag -> lvl15+stress
I think the idea is that the item should be a small gift or trinket from her master or another friend. It is "almost" a toy to pair with her spell; if it gets too powerful it kind of breaks the character, so it doesn't really needs penetration... By the same token, a friendly magus wouldn't care so much for the small payoff. For example, a magus could easily instruct an apprentice to enchant this item in a season that the magus is not occupied with his lab; or Lyrus could have enchanted the item for her because she was crying.
But yeah, from a practical point of view, Lyrus could have decided "well, I'll make something that will be more useful" and enchanted (or commissioned) an item for 2 or 3 pawns of effects (6~9 total cost if bought from a Verditius).
Side question: what is the sigil of the enchanter?