Update - This dealership (where we bought it) did a comprehensive inspection today (not just a test drive) Diagnosed the analog brake system (the usual -brake lines, master cylinder, calipers, pads, etc) But I'm happy they tested the ABS Control Module, valve assembly, and ABS pump (not done by the other place). The ABS module scanned fine, but as an electrical board it could be intermittently bad - the tech said it could be months to get one. The valve assembly and ABS pump checked out fine.
Apparently The Lifetime Added Care Plus Warranty only covers the issue if the dealership can prove a defective part.
If not covered the replacement of the ABS Assembly (ABS Module, Valve Assembly, an ABS Pump) will be around $2500 if they can get the parts
They want to keep it for another day or two to see if if they can replicate the problem to help out warranty and were concerned about my wife driving it