Elsa was a child overwhelmed by her Force abilities on a backwater world that did not believe in the Force; her parents shut her away from the world for years after she hurt Anna. Anna healed herself with her own Force powers from the incident when they were children, but the blow to her head blocked her memories and kept her abilities from manifesting further.

When Elsa runs offworld to escape to somewhere she can't hurt anyone, she runs into Rey. (Maybe her ship breaks down on Jakku?) Everything changes when for the first time in forever, she isn't viewed as a freak or monster, but accepted as a friend, albeit one with ridiculous and unstable Force powers.

Any pairing is fine. As a bonus I'd really like a scene where Rey is fascinated/dorkily happy at the sight of Elsa creating ice where there once was none.