Are you sure Yuki isn't in heat? Do you have plans to spay her soon? That would be my first suggestion.
When you were gone, who looked after the cats? Did they stay in their home? Sometimes when a cat's routine is upset, it can create a great deal of stress and this may be Yuki reacting with re-directed stress aggression. I would for sure keep Tigger and Yuki apart for a few days, and then slowly reintroduce them as you would a new cat. There are some descriptions here on how to do that:
http://www.catsinternational.org/art...ther_cats.html
http://www.catsinternational.org/art...roduction.html