Has she had bloods done to show how well her kidneys are functioning? EC is a real pain cos it can have so many different way of showing its-self. Personally I would agree with the second vet, as long as she is not suffering or in pain, and see how she goes with the panacur. It is said that a majority of rabbits have been exposed to EC and actually carry it without showing any signs. Sometimes it can start to show when they go through a stressful situation but some never show any symptoms.
I adopted a bunny who had EC, we eventually lost Shayla to renal failure, but she lived in my house with her husbun Max and he has never shown any signs - I panacured them both when she first arrived and then periodically did her to try and keep on top of it so yes, I do think once she is well enough, she could live with another bun.