As has been learned from the movie, rainbow guardians were supposed to choose students. Azura chose Elina. Who chose the other guardians? Here is a small diagram:
Ruby (red guardian) chose Shimmer;
Tourmaline (orange guardian) chose Sunburst (maybe she is his daughter, they are so similar in character! XD);
Topaz (yellow guardian) chose Linden;
Nameless green guardian chose Glee;
Azura chose the protagonist of the movie Elina;
Nameless blue guardian chose Lumina;
Amethyst (purple guard) chose Faban.
Well, I hope that my observations will be useful. In the near future I will make more meaningless topics, xD.
Your Lorinna / Lolita.