Should this job been advertised?

[MissQuery]

I have worked for my employer for 5 years, longest serving employee. I was supervisor for 2 years then was moved sideways to concentrate on one particular area of work which I was more than happy to do. When the supervisor who replaced me left the company a new position was created within the company and a fellow employee was moved into this post but as I had the most knowledge and experience I was expected to train her how to do her job yet she was suddenly being paid a lot more money than what i was but doing nothing herself and I had to then become answerable to her. Is it right that she was given this job and no one else was given the opportunity to do so. The only good thing to come out of this is that I have been offered another job elsewhere which I have happily accepted as I do not see why I should work for someone who does not know their own job!