well it took most of a year but I finally got my BRB to take a F/T mouse!
I had been saving any bedding that came with the live mice I was buying (and gassing pre-feed with CO2) and kept a baggie of it in the freezer. I put a frozen mouse in the baggie with the bedding and put the whole mess in hot water to thaw. ended up with a dry mouse that smelled to high heaven like the bedding.
She took it right away.
I had tried prescenting by rubbing a thawed mouse in the bedding but that didn't transfer enough stench to trick her. This new method seems to stink it up much better.
Hope this helps someone in the future :)