The answer to that one is fairly easy.
Just turn her into an actual Mary-Sue as opposed to a Social Justice Mary-Sue.
No seriously, that would have worked and fulfilled the stated (although lets face it, false) goal of getting more girls interested in Star Wars.
The complaint about Rey being automatically better at everything than any of the men in the original trilogy is valid. However, the problem is if she had been bad with the Force at first and was easily beaten by Kylo Ren in the The Force Awakens. Then went off to study with Luke as real master instead of…whatever the hell it was she was doing in TLJ. She would just be retelling Luke’s story. This is a valid criticism. However, ALL of the complaints against Ma-Rey Sue are also equally, (if not more) valid.
So what to do, if you aren’t trying to tell to Luke’s Story all over again and trying to get girls into Star Wars.
The answer is simple. They should have presented Rey as a genuine Mary Sue. She would have been special just for being who she was and everybody would like her just for her being her. Except for the bad people, naturally, that’s how you know they are bad.
But Cataline, what would she have done? You ask.
The answer is nothing. That’s pretty much the definition of a Mary Sue, she would have been special just for being who she is. I suppose you could make up some stuff about how important it was that she pick one side of the Force or the other but you really don’t need to tie yourself down to her actually doing anything.
Now I admit that sounds terrible because it is. But there is a big difference between something being terrible and something not making MONEY. If you think Mary-Sues don’t make money then you never heard of the Twilight.
The other element is that you would have to have two alpha’s fighting over her. Good Boy Alpha and Bad Boy Alpha. She would be torn between them.
It would have accomplished pretty much all of Kathleen Kennedy’s stated (though not actual) goals and not horrendously damaged the franchise.
But being inept storytellers they had Rey handily defeat her Bad Boy and put the Good Boy in the friendzone as a beta-orbiter, all by the end of the first movie.
That was as impressive as it was incompetent.
The Dark Herald 
Considering how much the 2 films stole so far some from the original trilogy, just telling Luke’s story as a girl would have fit right in with what they were doing.
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Should have set E7 900 years in the future, and called it “The Yoda Prophecies”. A 900-yr old Luke Skywalker is training the first Force-capable person (besides himself) in centuries.
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