Thanks, Twelvetigers, and thanks to those who have messaged.
Basically, sometime between 7:30-10pm last night she managed to get both hind legs pretzeled around a pipe panel. We found her covered in sweat, groaning, and basically in a lateral recumbency. Took about 15 minutes to get the pipe panel off and then she rested for about 5 minutes before deciding that since I walked over to the water bucket, she should too. Somehow she managed to get up and we then waited 3 hours for a vet to arrive. (how in the world does UCD only have ONE vet on emergency field calls??? poor woman had to deal with me calling every 30 minutes to find out if she was finished suturing her last case)
Anyway - long story short, it was amazing she was standing. Details are getting muddied up but if I understood everything correctly she had two different joints open and they were worried about sepsis because her temperature which was around 100, was slowly crawling up past 102.5. The big kicker, though, was that she also blew the ligaments in her stifle, and possibly had fractures in her front leg somewhere.
She was a super star the entire time. She is generally well behaved but she went above and beyond last night. She loaded sanely in and out of a huge step up trailer with a hip to fetlock splint on....she never reacted out of pain, never showed anything but love towards me. I received more nuzzles, kisses, and hugs from her last night than ever before. I always wondered if she truly trusted me or if she just put up with me. We were tuned in to each other from the second I stepped in the paddock to calm her down to the last minute she pushed her muzzle out to my hand as she started to lose consciousness.
What a mare. What a fantastic fabulous mare. Good bye, my sweet sweet Trinity.