If there is no easy way then maybe you just have to be up front and honest as to why you are letting her go. Tell her how much you've appreciated her work in the past, then point out that you are aware that she doesn't like change and the fact this new venture is going to require her to work some different hours along with some new responsibilites. Finish by saying that you feel that she should explore other opportunities that best suit an enviroment she is more comfortable working in.
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