@blueoddog Hello!
I will try to answer the questions, but bear in mind that I'm speculating just as much as you might be, I just happened to listen to the album this series is based upon ("Märchen", by Sound Horizon - if I'm not mistaken you'd be able to listen to the songs on youtube!).
More than the Evil Queen being her mother, I think that perhaps it's to hint to the idea that the cycle is repeating itself. The Evil Queen married the King, but the only answer he could muster was how the last Queen was the most beautiful, leading her to try to destroy all the pictures, garments and anything that resembled the previous woman - except, of course, her daughter, Snow White.
The little girl probably isn't the Wise Woman - that would be Therese von Ludowing (as far as I can tell, she was a noble who fled her house perhaps due to an unexpect pregnancy? Either that or the fact that Mär was an albino - that wouldn't be the first time a child with those features would be taken as "accursed", according to some theories, in the albums - even regarding one of the stories in this series - so to protect him she fled the house during the night).
Perhaps the nectar part is trying to hint to something like the King turning his eyes to the young princess, since she has grown to look like her mother as each passing day? That could be the way the Evil Queen refers to her "tempting" the King - and perhaps to allude to the fact that maybe Snow White wasn't as innocent as she looked like? (the way she starts talking to the mirror the same way as the Evil Queen and being focused on her own beauty got thinking) // (that is not to say that I would be escusing or blaming Snow White for "tempting" the King or anything; that's disgusting).
Hope to have helped! Like I said, I'm speculating just like anyone else after reading this series!