I’m sorry about the loss of your boy. That is incredibly frustrating to be turned away by the e-vets. 
Binky Free, Theo.
It was pointed out to me that she very well could have had dormant pasturella her entire life, may have passed it to Theo and something triggered it in him after 2 years, and his passing has triggered her pasturella.
I suppose that scenario could be the case, but it could also be that Theo was a carrier and passed it to Eve and her symptoms only presented due to the stress of losing her bond mate. Or it could be that both carried it as it is thought most are exposed to the bacteria at a young age. Or perhaps Theo’s death was not related to this at all, despite your having seen some respiratory distress. There are just so many potential scenarios.
Take things one step at a time and chat with her vet also. You have a good opportunity currently to manage Eve’s current resp. condition and it would then be less infectious (if bacterial) if you do decide to get her a new friend.
I believe there is a vaccine for pasteurella also, although I don’t know how widely available it is. Something to ask the vet about? If it gave you peace of mind, you could look into getting a new rabbit vaccinated…
That said, there are a lot of other bacteria that can cause same respiratory symptoms. Or even non-bacterial causes.