It's possible but it would be impractical. For Luzica to cast it there are a few ways to do this. A heart beat script will work but would be an unnecessary strain on the module and the host machine, and it could break they are not 100% reliable I am lead to believe. Also multiple heart beat scripts will be given different priority so there might be an issue there, not sure. The heart beat script will fire every 6 seconds, the script could tell Luzica to physically cast the spell, but she would run out of prepared spell slots very quickly, npc's have spell books like players do and there spells per day are set in the toolset. So alternatively you could create a script that fires invisibility purge at a location at certain intervals, or it could be triggerd at the doors once a PC steps into a trigger area. Luzica wouldn't be casting it, but the spell would be cast over and over giving the same affect, but this becomes harder to explain, who is casting it and why? What is the source of this infinite accourance? We could explain this as a mythol, but why would there be an ancient elven spell cast on this location and what is the power source of the mythol? If we where talking about Ellminsters tower then yes it would be very easy to explain something like this, it's a security measure that you might expect to be in place to protect the 1267 year old Cleric/Wizard/Archmage (and a rouge and a fighter), but it's not really possible to explain such a powerful mechanism for the Morninglord Church and the relativly low importance of the clerics inside the church. There is also a risk it would feel like an OOC mechanic to facilitate an IC rule. It's perfectly legitimate to cast invisibility and enter the church if your character has a reason to do that, so why would we prevent that from happening in such a finite way?
This highlights limitations of the engine that we just have to deal with, the NPC's are mindless sprites that can mimic a few situations fairly well to make them seem more life like, but at the end of the day we can't get away from that truth, and some things we just have to live with.