There's also something like using Yuyuko, or Satori herself.
For example, Yuyuko gets bored, and decides to leave Hakugyoukurou to mess with more people than just Youmu in order to alleviate that boredom.
I wouldn't imagine Satori around when Yuuka was young.
As for Yuyuko? She's be more sane than she is now back then, because her mental state is because she's been forgetting things over her 1,000+ years of being dead. Although newly-deceased Yuyuko could be interesting to use, I would see her as pretty much a totally different character, far less eccentric.
Just to put into context, if we're looking at 'Young' Yuuka, I'm thinking 1,000+ years ago. There's enough characters known to be 1,000+, like Byakuren and Yuyuko [Kinda]. The Taoist crew I think were around back then too.