Hmm. I think this was addressed in an interview with one of the guys that worked on the show, wasn't it?
When they talked about the Show, they said the Masters would be fighting the good fight against Hordak much like the ol' Rebellion, and that She-Ra would have been featured.
They said she wasn't going to be his sister tho... But some other relation. And I think there may have been talk about the future...
My memory isn't the best, but I think she would have been He-Man's daughter from the future, and either have guest-starred in a time-travel ep, or seen in a flash-forward ep, "what if the Horde will never be beaten?".
Altho I feel it's anathema to the character to be featured in such a way, it actually has some logic too it. It would certainly be easier to introduce her then, and this would explain why she has different powers than He-man.. Not just super-strength and invulnerability, but healing and telepathy too. Among other things.
Sounds a bit like a combo of He-man and the Sorceress powers, doesn't it?
I'll try to find the interview, because it could be that the half of this that isn't guess-work, is actually just a hallucination of mine.