Transitions

My younger daughter has never really been "diagnosed" with anything, well, except when we moved a few years back. The doctor slapped a Post Traumatic Stress Disorder label on her chart then... We talked about OCD at the time, as she handled her stress about moving with going a little germphobic, washing hands and cleaning things compulsively. As she adjusted the obsessions subsided, thankfully. But transitions have always been hard for her. She likes things to be predictable. She likes the same, the same, the same. We were just on vacation for a week, and the first two days were hard - meltdowns and tears. The rest of the week was good - she had fun. As we prepared to leave -meltdown city again. As she's gotten older the transition meltdowns have become a little more manageable, not as all encompassing, but I still feel bad that I can't seem to help her head them off. Ideas?