I think she has to be Luke's kid. Him and the mother get separated for whatever reason, the mother gets taken, and she gets sold into slavery on Jakku.

>She's Kylo Ben's younger sis. She also was being trained.
>Bitch Boy Ben cuts down the Jedi (probably on Snoke's orders),
>but can't bring himself to chop his sister. So, knowing he
>can't say he left her alive, he drops her on Jakku to work
>knowing she won't be able to get off world. Leia and Han think
>she was slaughtered as well which is why they don't recognize
>her as their daughter. But they both seemed to sense
>"something" with her it seemed to me.

Eh, problem with that is that they seem to be roughly the same, if not similar ages. So she'd remember more about her brother or her family if this was so. It would make Kylo's "You see Han Solo as the father you never had..." speech a little superfluous.