De-witching progress on a communication front is no longer dependent upon incarnation of one form or another!
First, we need the soul to be sane, and it looks like we are getting close to a result that won't scorch our brain next time.
We have the copied Soul Powers, and that should get us a minimum required level of success. The question is how to use them. If we can train to use one of Sayaka's gems without her, we de-couple a few issues.
As far as determining the form of a given resurrectee, simulation has to be the best concept. In a mental construct, or in a barrier, producing the facsimile of a body image from an active consciousness should be easy and safe. That can double as an adaptation training session too.
Niko can fabricate bodies, my only reservation is that we haven't asked if doing such in Japan requires millions of gallons of ultra-pure water, or if that only applies to human tech cyborgs.
But seriously, her base material could literally be about 130kg of chicken eggs, and a pinch of minerals.
The way to connect almost any suitable being to a body is already here. Mami might be well able, but she doesn't have to do it for us.
Sabrina has the
Control Enchantment.
It was expressly named. With a bit of level grinding, I expect all we have to do is enchant some viable substrate. Such as a body with no soul. Our intent is the key. If we study what the Incubators equipped us with, we can grow our magic into the human-style nerve analogues we have seen. Then we just will it "to be under the control of her." Put them in contact, and watch the miracle happen. With time, an active magical soul should take over the upkeep.
If we really want to start out with a witch-girl right now, we can just make a literal clay golem. No complication from using Grief. A quiescent Witch is still not quite a girl. I expect magical therapy prior to reincarnation will make the experience more pleasant for both of us, however.
So are we gonna make a Grief Toucan body and give it to Aurora already? I've been waiting years for this.
If you are willing to use clay, toys or wood, I could see this as a step forward. Grief has a few extra cautions associated with it, and our end-result is supposed to be mundane flesh. Will you barter away the material?
My best approach is to keep at it until we have enough hope in the core to re-form a proper Soul Gem. To get there in reasonable time requires a large Hope-enchanting ritual.