We lost our senior girl to osteo 3 years ago, but we had the opposite problem. We didn't know she had osteo until the day she came limping down the hall. She screamed in pain and we were at the vet's office within 15 minutes. The x-ray showed it was already in her ribs and in fact had broken one. We had to help her cross the bridge that morning.
We had no time (less than an hour) to prepare ourselves and were so full of guilt because we didn't realize that she was ill.
We didn't go through the hospice care you had to provide, for which I commend you, but I wish we could have had that extra time with her before losing her. On the other hand, her pain was short lived for which I will always be grateful.
It will never go away, but it will get better.
Hugs...