I am wondering if it would be possible to have her taken to surgery and have a c-section performed, hopefully save the foal, less stress on the mare. I know the trailer ride won't be comfortable for her, but maybe the vet could give her a morphine injection that would help relieve the pain for the duration of the ride. A scheduled surgery would be very safe, clean and more than likely your mare would recover and be able to still retain her reproductivity.
I too had tears watching your loving hands massaging your poor mare last night - I am sure that you are very worried and scared -- my prayers for a good outcome for your precious little mare.
Hugs (((( )))
Stacy