I'm going to go with he Luke theory.
Not only does she seem to have a peculiar affinity with Luke and Anakin's lightsaber, but her "origin" closely mirror's Luke (Taooine) in more ways than one.
It's not that far fetched to imagine that, being hunted, Luke and her mother left her behind in the most unlikely of places (junkyard), but with someone staying behind and keeping an eye on her from affar (imo Von Sydow's character. Who also happens to have Luke's map). This mirror's Obi Wan staying behind to keep an eye on Luke, and eliminates mostly the "random" factor in many ways (he would live near her camp and the particular junkyard she happens to work at) with BB8, Poe, and Finn, just hapenning to end up near a powerful Force Sensitive Woman who just so happens to be in tune with Luke's weapon.
If she had been one of Luke's students, ad I've read, Kylo would definitely know her, while it would make sense for Luke to isolate her from students who may turn dark. Her parents may have also wished to avoid risking her following in the footsteps of het grandfather.