Although I am trying not to dwell on it, I believe we have days or weeks, not months or years before she will need to be put down. .
I think we're all missing this sentence here.
If you believe this is end of life care and are just making her comfortable, the I would probably not do the BW. If I saw major improvement that would make me change my mind on this, then I would take her back to get the BW done.
The organ function BW is not that expensive but if you think the money is better spent elsewhere to help her be more comfortable then that might be the better option.