OMG I just went through something very similar. I just picked up a new pup on Friday, last week. Saturday morning this poor little girl's stomach was growling and such a bad case of diarrhea I have ever seen...
Then the blood started. Chloe is 4 months old and has had all her vaccinations. So off to the vet's office... She had a really bad intestinal infection.
Poor girl.. They put her on two antibotics mixed into Albon. By the next morning her stools were already firming up and no blood. Chloe is doing much better.
Hope all goes well for Trixie, I will be praying for Trixie a speedy recovery.