Im doing a masters in Art therapy. Im not sure how the job scenario would be for it moving forward. However, is it ok to do a second masters in educational psychology?
It is certainly ok to get any degree for which you are qualified. I don't know why you might question that. Whether there is a better path to your life/career goals no one can say. To me, who knows little of either field, they would seem to complement each other for some kinds of professionals, actually. But you can also get a doctorate in clinical psychology, I know. You might look at that.
But what it takes is to apply to some programs and get accepted. Write a good Statement of Purpose for any proposed degree, explaining why you want the second degree, no matter what it is.
I suspect you can have a career in either field as a private practitioner, though you may need a license from some government to do so.