My .02
I use CS2 every day. It is a rather complex program with a great deal to learn. In Catherine's case she has seven months to work with it. In those months she may be able to take a PS workshop or two that will enhance her learning curve while in Bali. If the class is going to use it as the defacto program, then by all means spend time with it before hand. One less thing to learn, when she will be given a mind bending amount of other info that will invariably change and enhance her visual skills. Not working with it before hand is sort of like saying "Don't worry about your bouyancy skills. We'll teach you how to dive too." She should task load in the areas that she can't teach herself and the more advanced skills. One of those areas is creative and to a certain degree u/w lighting. If she has the basic skills down on CS2 - then topside and U/W she can be pushed in new areas.
Do you need CS2 to be a good photographer? No. When I started out as an advertising photographer, people would spend hours retouching a dye transfer print vs. now being able to do it in a matter of moments in PS. It used to be that a computer was only used for billing. Now as a pro, I have much more on my plate. It used to be that I only needed to be able to come up with a creative solution to a visual problem. Now I do that, plus I'm my own photo lab, data baser, stock photo house etc...
Where Catherine is at with her photography is at the steps of being a pro. CS2, a good computer, and a well thought out data management plan will save her time and money down the road.
Catherine - I don't mean to sound insulting, but if I were to compare you photography skills with diving I would say that you want to become a cave diver. You have many of the skills already and some of the gear. To become a pro photographer, you will need to get DIR-f'd. So some new equipment, some new skill sets, some business knowledge, some computer knowledge, some archival storage knowledge and you will be well ahead and on your way.