Poor lady.
Sadly, it is the case with vaccines that they can not be 100% effective. But at least rabbits have a specific vaccine designed for them.
When I had ferrets there was no vaccine designed to protect them from distemper (still isn't) and you'd have to take your chases using the dog vaccine off licence. You'd risk losing them by vaccinating them, or by not vaccinating them. And even vaccinated ferrets weren't protected from distemper as it reacted differently in a ferrets body to a dogs.
They will make progress on rabbit vaccines as VHD mutates, so we will always be able to provide the best possible care.