Well for heaven's sake it wasn't the foot drop at all! I got my referral to the orthotics place and hauled in all my devices: that is, the AFO, the bungee cord Dorsiflexion Assist, the Bioness L300. What I thought I wanted was the carbon fiber Allard device, possibly with the hyper-extension control that attaches to it, making it a combo device.
What I learned was that people with MS often progress into knee hyper-extension. Apparently it is a very stable position to have your knee locked like that, and we, being tippy and tippier as time goes on, just naturally want stability. Imagine that!