Well, there's good news and bad news, neither dramatic. Bad news first - the vet doesn't know exactly what is causing Halo's lymph nodes to be so swollen. The good news is that he doesn't think it is serious, and it is likely either allergies, or just a baby "cold" of some kind. She seems fine, and is alert and happy. Unless her lymph nodes get very hot and large, he says she's cleared for her move this Thursday. Phew. I should be getting a report of some kind by email that I can show to the new barn owner.
This morning the current barn owner sent me this picture of my goofy little mare: