Pyometria basically just means "infection of the uterus" and can be caused by many different bacteria. In rabbits, it is most likely to be caused by Pasteurella Multocida. I think with her having had a rough delivery last time, she may have retained a placenta or damaged something internally that allowed the bacteria to flourish. It is not *likely* that your buck could catch this, but I would make sure to disinfect everything that you used to necropsy her and her cage area and feeder/water bottle or crock, just in case. Sorry you had to do this, but at least now you know and she isn't suffering any more. {{{hugs}}}