Poor girl, I hope your hen gets better soon! Has the rooster also hurt the other hens? Unless you're breeding and need the roo for that, I'd seriously consider getting a new rooster.
Until now, only one of my bielefelder hens died (she was still young, around 25 weeks maybe) but I don't know...
I have two bielefelder chickens, too! I can't say anything about the roosters but my hens are really sweet. They are pretty docile usually and when I introduced two new hens last summer, they only chased them around a bit for the first two or three weeks and after that returned back to being...