Perhaps too obvious, and that wouldn’t explain from a genetic standpoint how she could go head to head with a far better trained individual from essentially the same parentage, true?
Mind you, she could have a mother that’s also powerful that hasn’t been introduced, but right now the only known character that may be living that could have given her that much of an edge would be Snoke/Plagueis.
I like the ‘Rey is Luke’s daughter but was enhanced in vitro by Plagueis’ angle best myself, but it’s not the only viable one. It’s just not a sure thing that she’s ‘just Luke’s’
Heck, she could even be Kylo’s with the age difference, he’d just have to be a VERY plucky young lad.