For your real question: just give it to her.

You already like the concept, you already want to do that, you already have the mechanical and story parts, and you already know there isn’t any magical-places system to fit this in. There is no need to create or discover such a system, then use it to back into an answer you already have.

For your general speculation on why Pathfinder and D&D 3.x don’t have unbounded, roll-your-own-artifact effects available at relatively low levels: because it is isn’t that kind of game.

D&D and derivatives are games that fundamentally grew out of adventures where you kick down dungeon doors, murder or sneak past everything inside, and stuff loot in giant sacks. As a system, they handle small-unit/SWAT tactics well, and everything else poorly. I have a lot of fun in the space it handles poorly (necromantic industrial revolutions? Yes please!), but they break really fast.

I am not convinced that it is possible to have a balanced game that both (1) uses rules, and (2) allows for powerful, arbitrary magical effects. Probably the closest system I’ve seen to what you are looking for is Exalted 2E’s manses, but Exalted simply does not care about balance: the core game assumes you are playing one of the most personally puissant entities in existence, so it doesn’t even matter if your house makes you immortal.

For your real question: just give it to her.

You already like the concept, you already want to do that, you already have the mechanical and story parts, and you already know there isn’t any magical-places system to fit this in. There is no need to create or discover such a system, then use it to back into an answer you already have.

For your general speculation on why Pathfinder and D&D 3.x don’t have unbounded, roll-your-own-artifact effects available at relatively low levels: because it isn’t that kind of game.

D&D and derivatives are games that fundamentally grew out of adventures where you kick down dungeon doors, murder or sneak past everything inside, and stuff loot in giant sacks. As a system, they handle small-unit/SWAT tactics well, and everything else poorly. I have a lot of fun in the space it handles poorly (necromantic industrial revolutions? Yes please!), but they break really fast.

I am not convinced that it is possible to have a balanced game that both (1) uses rules, and (2) allows for powerful, arbitrary magical effects. Probably the closest system I’ve seen to what you are looking for is Exalted 2E’s manses, but Exalted simply does not care about balance: the core game assumes you are playing one of the most personally puissant entities in existence, so it doesn’t even matter if your house makes you immortal.