Re: Did Rita create the Mystic Realm?
 

The Mystic Realm is like a pocket dimension of Earth. Its likely that it was created by powerful wizards and magically separated from the rest of the Earth. Perhaps Zordon gave her the role of Mystic Mother or intended for her to have it when she was purified.

Re: Did Rita create the Mystic Realm?
 

Rita created dimensions or had some in her pocket. This was shown as early as season 1. So I am not surprised at all she gained power in the Mystic Realm.