Indeed, if it comes down to having to pick the OS based on what software package(s) you need/want or might need/want in the future because of what a coworker/costudent did/does/wants to do, then I'd start with a Mac laptop. You can virtualize a machine (or three) if you need Windows, Linux, BSD, whatever other environment available, but AFAIK for non-Mac hardware there is no (legal) way to run OS X. Load it up with RAM, make sure you have several large external drives for backing up stuff, and off you go. If you knew you would absolutely never need OS X based software then get PC based and shop based on percieved hardware quality and warranty.
As to her study abroad stuff, may want to make sure whatever she ends up with the warranty can be used wherever is she is going to physically end up wtih the device. Would suck to be working in Europe but need to get a service call from the US, or having to ship back and forth for repair...