It was a filly, kind of smutty buckskin with 2 high whites on both back legs and a huge white star, like Mom's. A little small due to prematurity, but otherwise normal.
Vet's diagnosis was "placentitis" as the placenta was enlarged....was, in fact, the largest she said she'd ever seen. She palpated and found that everything inside Mom was fine, nothing left over, no retained twin, uterus shrinking perfectly, etc. Gave her some banamine and oxytocin, and recommended not to breed her back on foal heat, but to wait a couple of months just to watch her. I was going to let her skip a year anyway, so that's fine.
Sigh. My heart is broken. My first mare, my first baby. It's been a lousy 2006.