Many times patients are open to conversion to bupe products if you educate them about it. If you talk to her about bupe and she doesn't want to do it, then I would pass, and say something along the lines of "This is the only opioid I would recommend for you and I understand that you are not interested in it. I think it will be very difficult to find anyone that is going to continue your current regimen. If you change your mind please let me know and I would be happy to start/talk more etc." or if you don't prescribe bupe change it to "happy to refer to someone who prescribes...."
I agree with others, I would use suboxone/subutex. I don't think belbuca is going to be enough, especially if the 100mg of oxy has been a long time going. even if you wean it the tolerance doesn't reset that quickly.