Is it possible to get the BO and vet in the same place at the same time? Having the three of you looking at the horse and having an open-minded discussion regarding the plan of care for the horse could really help.
As an owner, you are the one who calls the shots because this is your horse and you are the one paying the bills. It is your prerogative to take or leave what the vet says. You as the owner set the standard of care. But it is not the barn owner’s prerogative to make the decisions for you; they should be deferring to what you, the owner, want for your horse (barring any abusive, dangerous, etc. situations).
I understand that you are grateful to your barn owner and staff for lots of help and don’t want to burn any bridges. Straight forward and transparent conversations will cut out the need to cater to everyone’s emotions. Keep things simple.