I'm not sure if she's as "potent" yet as people seem to think. Yeah, she reversed Ren's probing. She mind controlled a Stormtrooper (ones who seem more susceptible given they're raised just to be soldiers and follow orders). And she grabbed the lightsaber when Ren was trying to get it. But what if Ren's not that good with the probing? It took a lot of effort to get from Poe that he'd given the map to a droid, but no details on the droid or where it went. And when he was trying to get the saber, he'd just been through a fight that took a good bit of energy and was wounded pretty badly. Plus that whole thing with Snoke commenting that he hadn't completed his training yet.
Maybe she's strong, but we haven't really seen evidence that she's super powerful.
Her being a nobody makes for a more interesting story, and I'd rather go with that (well, not exactly "nobody," because likely someone relatively famous dropped her off), but I'm a bit concerned they'll feel a duty to have the Skywalkers be central to the plot because the core Star Wars story is essentially about the Skywalker line. Then again, Ben/Ren fills the position of a Skywalker kid (being Leia's child and the grandson of Anakin Skywalker).