I'm a bit confused at Nina actions. she knows Mei has a thing for Yuzu and yet, she encouraged Sara.
Nina seems to be a bit of a villain here. Yes, she loves her sister, but like she said, no matter what it takes, she is going to fulfill her sister's destiny. So, I doubt she really cares about the relationship between Mei and Yuzu, she is going to take advantage of their troubles so she can get Sara and Mei together. Sara however, seems to be a good person and I think if she found out what Nina was up to, she would be pretty upset.