The rules are not tailored to your server or its current population. The rules are for everyone, on all servers. If you expect Funcom to care for the fact that almost everyone on your server was okay with the situation, that means you expect Funcom to have an admin assigned to take care of the community on each server. And that costs money. If we paid subscription to access official servers, that would be a perfectly reasonable level of service to expect.
But even if they did have an admin per server, is it really okay to ignore the rules and tolerate spam just because everyone currently playing on the server is okay with it? When I decide I’d like a fresh start, with a new character on a new server, I go and look for a server that looks decent. If I find a ton of spam, I skip the server, because I’ve had enough of that crap. And I’m not the only one, either. People are tired of spam, and they’re tired of servers being slowed to a crawl because someone thought it would be fun to build a replica of Taj Mahal and fill it with all sorts of animals.
Did you, by any chance, mean this:
Because that’s the only rule that has been conveniently absent from all of your complaints about how “anything could be spam”. 
It starts when you block any resource. When does it become ban-worthy? That’s decided on a case-to-case basis.
Does it lead to loss of performance on both client and server? There’s never going to be a “sweet spot”, because it’s never been about how many pieces you place, but how you arrange them. You could do more damage with fewer pieces, so precise numbers are meaningless and would only lead to more “rule lawyering”.
Hey, I’m not the one who implied that they banned her because “she made like 2 lines of foundations around her base”. That was you.
Looking at the pictures, I can’t see anything that I would even report as a player, except for that pillar spam behind the altars. But I’m neither a player on your server, nor an admin, so I don’t know what happened here.
And that seems to be the real problem. Did they ban your girlfriend for spamming? Did they ban her for building in a way that causes performance problems? Did they even explain why they banned her? From what you wrote, it sounds like you don’t know what’s going on, either.
If you asked them for ban information and they didn’t answer, that’s not okay. If you asked them, but their answer was too vague and unclear, then I agree they should be clearer, like I’ve already said.
But if you say they banned her for a specific reason and you don’t really know it was for that reason, then don’t be surprised when people question you or point out that it sounds like a valid reason. 
And as I already said, it doesn’t matter that “everybody does it”. History is littered with things that everybody thought were okay, but weren’t.
However, if the land claim prevents you from repairing or replacing things you’ve already built, that should be reported as a bug and they should fix that bug. And if someone is abusing that bug to harass and grief you, then that someone should be reported. They’re not only abusing the claim system, they’re actually exploiting a bug.
Are we really gonna do these hyperbolic metaphors again? This is getting old. You didn’t get a death sentence for parking your car wrong, you got banned from all Disneyland parks because you pooped on one of the rides in one of their parks.