Sorry, dude. I'm not particulary using the nodes, so maybe there are some "modern" expert would give you an answers. Though historically speaking, the nodes originated from Persian and then transmitted to Indian. There was a Britsh astrologer, named Sir William Lilly (17th Century CE), who refered South Node and North Node as Dragon's Tail and Head respectively. The book is worth for reading and it's also free.
Yes, south node represents area of life that we have already achieved in past life. When we are assigned a work where ever our south node is placed we will do it with minimum effort or supervision. But we will not enjoy doing it. Because we are born to do do what our north node represents. It represents our desires of this life. And we are still in learning stage regarding the life area represented by our north node.
It's funny because I've read on many sources basically "SN = BAD" and "NN = GOOD" and I used to actually believe that until experience haha. I wonder where that comes from.
Familiar, okay; still trying to explain the fascination, like she has something I'm missing.
That's probably not really a south node question. If you feel like someone has something you're missing, the most likely astrological explanation is that their chart completes yours, in some sense. Maybe they have lots of placements in elements where you have little or nothing. Maybe a part of the zodiac that's empty in your chart is occupied in theirs. Maybe your temperaments, which can be calculated based on certain chart factors, balance each other.
This could be so even with the familiarity you describe, and even if the explanation that you've been together in past lives holds water for you.
People the same age always have nodes conjunct each other's. That alone doesn't explain the attraction, or you'd have that with all your classmates. Moon on south node adds a strong note of familiarity, since not only can south node represent the familiar, Moon definitely does.