[lcstorc]

Sorry to hear about your loss. I too would have removed the nem. If available I would have put it in a separate container but you were definitely right not to leave it in the tank. Anytime you are dealing with a nem that you don't know if it is alive or not, you can always do the smell test. The smell of a dead anemone is not something you forget quickly.
You mention that the amonia was elevated from what it had been. There should be 0 amonia, 0 trites, and 0-10 trates for at least 6 months before even attempting an anemone. Also, as Al mentioned you really don't have the lighting for it. Anemones have a very very slow metabolism and can take months to show the effects of a long term problem.
The partially good news is that RBTAs are know to be tolerant of relatively low lighting. I have 2 in my 20g tank with T5 lights. They have moved to the very top to be close to the lights but seem to be doing fine. The only reason I have 2 is because mine split which is not necessarily a good sign. They will split either because they are happy or because they are trying to double the chances of survival by producing a clone. I mention this because many people thing their nem is doing great because it split.