We just buried Oreo. Please read. I don't want to lose another.

My tiny Oreo died yesterday. In my earlier post, I explained how she hadn't been herself lately. Yesterday we noticed that her tail looked broken. We have no idea how that could have happened. We didn't notice it the previous night. She had become so, so frail and tiny. We had started her on Baytril a week earlier, and reintroduced Tetracyline after taking her off for a few days when she seemed to decline suddenly. We rushed her to the vet. He confirmed her tail was broken and said she was probably in a lot of pain, but in her fragile state of health, he did not want to amputate the tail. He felt she had a serious heart murmur. He injected her with Gentamicin. It took three attempts because the needle kept passing through her skin. She was probably only about 2 ounces. He told me to give her the Lassix I had at home for the heart condition and continue with the antibiotics that evening. She didn't make it that long. I held her about an hour before she passed. I was checking on her frequently and she clearly wanted to be held. I had no idea she was so close to death or I would have held her and stroked her as she slowly passed. Instead, I put her back in the cage. The next time I checked, she was gone. She looked like she had passed while sleeping. One strange thing. My daughter had noticed that she had isolated herself from her companion Missy the night before and never returned to their igloo all day yesterday. They are usually always snuggled together. Is it normal for them to do this if they are seriously ill or do you think it was just uncomfortable in there for her with a broken tail? Now my concern, what about Missy? She seems to be doing much better, after being on the brink of death in February. I was planning to continue treating her with Tetracyline. I noticed that my vet had combined the Tetracyline with a steroid called dexamethasone. That scared me because on the drug usage chart I got from the Rat & Mouse Gazette it said that you should use the dexamethasone only for short periods. Both rats have been on it since February. I expressed my concern to him and he felt that there was nothing to be concerned about. He uses it for extended periods all the time with dogs and cats. He said if they were becoming obese, it would be a concern. He did say that I should taper off using it rather than quit cold turkey. I didn't do that two weeks ago when all looked well and I decided to try eliminating all the medicine. That was when Oreo started her decline. He said Missy probably doesn't need the dexamethasone any more, but I should gradually decrease from twice a day, to once a day, once every other day, etc. and then just continue with the Tetracyline. Does anyone have any experience with that steroid? I still question whether my tiny Oreo should have been on it so long. She was a sneezer, but never had any serious respiratory problems like Missy. I'm just so puzzled about this sudden death. Thanks for listening. Sorry to go on so long. Any advice for my remaining rat is appreciated.