15 year old with LD

I just needed a little guidance from some that have already taken this path. There is a strong possibility that I will be taking on the education of my 15 year old niece. She is dramatically behind in her studies and has major esteem issues from a life in public schools and not measuring up. I know a lot is the “method” PS use that has her stumped, because when I employ living books & narration with her, she retains very well and excels.

As my brother finalizes his decision (and I pray he lets me HS her) I am preparing as if she would be joining us. I have a 6 & 7 year old entering 2nd grade next year. In many ways, my niece is about that same level. Would it be additional harm to her if I added her in with my DD’s? Would she feel worse being in “2nd grade” again? I will enhance her studies on the subjects, of course, but she’s so beaten down, I’m not wanting to hurt her further. Would that give the impression she’s in “2nd grade” even if she’s getting different work?

I do not know what her LD is. It runs through my SIL’s family, at least half of the children have it. Severe lags in comprehension, speech issues and delays in maturity. Those that were allowed to attend charter schools or classes designed for them, were much more successful then my niece has been. She’s had to live most her life on a military base in Japan where the options were limited. Back in mainstream US schools have all but devastated her.

Any suggestions would be welcomed. My heart wants her with us, but it’s in God’s hands. If she does join us, I pray I am able to meet her needs.