Hi - well, rootball aside for the moment, I have an idea that the foliage is hardening due to a much higher frequency of watering than would be called for in junipers, whether or not they live outside or in. They're not houseplants and as natives to high, windswept semi-arid areas, do not need watering often at all, though it should be well done when done. Why the rootball is sitting so high I can't say - are any roots exposed apart from ones near the trunk that have already gone woody?

Bonsai are normally planted so that they do sit a bit higher than the rest of the soil, but not to this extent. I wonder where you wife got the tree - and ask because there's always a glut of cheap Chinese imported ones sold everywhere from the back of a truck to Wal-Mart, etc. with either tags printed with instructions completely unsuitable for the tree (generic, not species specific), or no tags at all, and it's a real shame, as only people with experience in bonsai should ever touch them. They do need to live out for their lives, to experience all seasons, including cold dormancy for months in fall and winter, and while knowledgable growers may get away with them in Arizona, they'd still need particular locations and special care to thrive there. I'm sorry, but regardless of how long they stay green, once they go brittle, they're usually long gone. If you like bonsai and want to grow some, start reading, learning, etc. about the different types of material available locally (nurseries) and how to take care of them and turn them into bonsai - you'd just buy young plants/trees and take years to do it - it's not an instant hobby.