Should I have euthanized?

We put my dog Kyra to sleep yesterday and I am struggling with the decision. Here are the facts leading up to this... She is 16 years old. For 2 or 3 years we have been giving her 75 mg of Rimaadyl per day for arthritic neck pain. If we don't do this, within 4 days she develops a high fever (106 typically) and will not move. She just lays in her bed and shivers. This has happened twice in which both times we had to take her to the ER to bring her fever down quickly. We were told she will have to remain on Rimadyl indefinately, which may cause serious side effects, such as kidney failure, however due to her age, it is a trade off to keep her comfortable. She always seems like she is in arthritic pain. She drinks a lot of water. On Friday she had terrible foamy bloody diarreah. This happened for 3 days. Her water consumption increased significantly and she wanted water constantly. She seemed very aggitated and in pain. She was aggresively licking my other dog, pacing or drinking. She just wouldn't settle down. After 3 days of this we decided we just didn't want her to be in pain any more. I had made up my mind it was kidney failure. Yesterday we went in to the vet to put her down and he felt her stomach and said he didn't think she had kidney failure. This little bit of doubt changed things for me, but my husband still strongly felt like we should put her down due to her level of pain. We stayed with her while this was happening. Now I am so consumed with guilt that I feel like I need to know that she was seriously ill, or else I made a huge mistake. Rationally I know she was in pain and probably wouldn't have lived much longer, but I'm still feeling so guilty. Based on what I have told you, do you think it sounds like kidney failure?