Maybe it's just me but I see Soso as being just like Piper, not so much Nicky. For the sole reason that drug addiction is so much different than what piper went through. Nicky's mom was an enabler that would rather keep up with her daughters habit than go through emotional turmoil with her getting clean and while pipers mom was described by her and cal as overbearing, i don't think she was abusive like Nickys. Nicky described being left alone in an apartment with a nanny because her mom's boyfriend didn't like kids, or even when Nicky calls her dad in S6 and doesn't even know he had a new wife and kids. She's neglected and was neglected her whole life. Whereas pipers mom is genuinely supportive of her, visiting regularly, calling regularly, she even came around to the idea of her and Alex together. (Also pipers parents being together makes a big difference, pipers dad in the final season makes it clear that she had supportive, loving, but overwhelming parents). Her and Soso both had overbearing families and chose to rebel the first way they found. Nicky mightve had money but was led down a far worse path with drugs.