My dog gets plenty of outside breaks. Sometimes I leave the back door open.
She insists on pooping on my bed. She knows it is inappropriate. How can I
make her stop.

No, your dog does not "know that it is inappropriate" to foul your bed.
Dogs cannot make moral judgements.

If she can't get to your bed, she can't defecate on it. Close the door
to that room and she can't get in there and onto the bed.

Take her outside to do her business and keep her there, on leash, in one
place, until she does it.

Jo Wolf
Martinez, Georgia