Looking at this from a software development point of view, such a sudden change does seem... unusual. I'm going to try and prevent as many assumptions as possible but I make no promises.
We know that Sarah knew about this change in advance of her tweets, as evidenced by the G+ comments this Monday. However, from reading those comments she, at first, appeared to be a little upset by the prospect anyway, potentially due to it limiting her time to interact with people? As a software guy with a client facing role myself I know how that can be, I get really grumpy when I'm left at my desk without any chance of interaacting with my clients, as is one of the curses of extroversion.
What we don't know, however, is what she's been moved to, whether it be ED related or otherwise. However, for it to be something related to the Gamescom reveal seems... unlikely, and this is where my assumptions and inference is going to begin. Gamescom is roughly a week and a half away, dev updates and other communication intimates that this is something that has been wroked on 'for a long time', one would assume that the project manager for this task would have gathered the requirements for the reveal and planned well in advance when they needed what resources, and could have informed people earlier.
For someone to be pulled onto a project so late in its life cycle seems... unprecedented. If they desperately needed something for Gamescom, they would have given her more warning and time to work on it.
From my interpretation of the information available, I wouldn't be surprised if Sarah's distress that we're seeing in her posts stems a lot from the fact that she enjoys interacting with the community - something she will not be able to do while on this new secretive task - and that she had become invested - and rightfully so, in my opinion - in her current project and was, despite advance warning, upset that it had to be shelved - or worse - handed over to someone else on her team. I know for a fact that the latter is actually MORE upsetting, at least for the guys I've worked with and have experience dealing with...