How terrible. I'm close to tears just reading it. I know how hard it is to wait 11 months for a foal and lose it but I can't imagine what you went through trying to remove it. How traumatizing for you. I am sooooo sorry you had to go through that. I don't know if I could. (hugs)
One of my mares absorbed her fetus which was discovered when the vet came out to confirm the pregnancy. She had a large lump in her uterus and the vet put her on antibiotics AND infused her uterus with some kind of antibiotic liquid. For the life of me I can't think of what the name of it was. Ask your vet. He/she might know what I'm talking about. I'm sure her uterus has some abrasions from trying to get the foal out, and the antibiotic infused into it would probably help keep the infection away.
I hope your mare pulls through this. It would be even more devastating to lose her.