Metacam safety questions.

Please can you advise regarding the use of Metacam injection with other drugs? I am sorry this is long winded, I wanted to explain what happened.
My cat, Rio, approx 14 yrs, had salivary cyst/cysts for many years. These fluctuated and she displayed no ill effects, eating well, going out, hunting etc. By the end of July last year, the cyst became hard and although her meow became husky she still ate well etc. She had a fine needle aspiration and only lymph cells were found. She was given an injection of Voren 14 50ml, of a quantity of 0.40. This was followed 4 four days later by an injection of Depo Medrone V of a quantity of 0.60. The only difference was that some swelling went down but appeared somewhere else on her face.
This year, although eating ok, she began pacing round the garden. I thought she couldn’t pee or poo. She could not settle in her chair for very long and would get up frequently. I eventually saw her toileting ok. After a few days she seemed worse and I took her to the vet. He gave her an Amoxypen injection on the Friday. On Saturday she seemed more settled and slept in her chair for much longer periods. Sunday morning she was pacing again, distressed and trying to find dark corners. I took her to the vet, on call out, and saw a different vet. He gave her a Metacam 20ml injection of a quantity of 0.10, followed by a Convenia injection of a quantity of 0.27. He said if she began panting to ring him. She didn’t pant but by Monday she was very distressed and was going into corners and pressing her head against the wall. I called the vet for a home visit. He said she had a very bad headache and that was why she was pacing and pressing her head on the wall. She began panting and crying whilst he was there. He said the swelling may have got into her brain. I asked him to put her to rest so she could be free of all this pain and distress.
I know I cannot bring my dear Rio back, but wanted to know about Metacam. I have read that Metacam should not be given at the same time as other NSAIDs or antibiotics but that 24 hours should elapse before other injections should be given. That Metacam is for pain relief for pre- or post-operative procedures so why was it given it for a swelling. Also that Metacam can give blinding headaches. Is Metacam another name for Rimadyl? The vet said he was giving her Rimadyl although I said I didn’t want any of my animals to have it, he said the injection was ok and it was the tablets that weren’t.
I would appreciate any information you can give me on Rio's case, especially regarding the usage of Metacam with Convenia and a short time after an injection of Amoxypen. Thanks very much, Jill