Just let her be, let her go through this "journey" she has set herself on. Eventually she will come out of her crisis, and may find her way back to you. I imagine she is finding it hard as well, but like them all, they seem to have to stay on this course, until it's done.
We get so sentimental at this time of year, longing for the perfect family togetherness, that it's no wonder it seems all the more painful when things like this are happening.
