I beleive (but not 100% sure) she lives quite a way from the BE office and has had enough of the travelling as she's been doing it for years. Think I remember a friend telling me about a month ago that she was leaving (she knows Winnie)...
I think she's decided that she's been in the eventing world for a long time and like mentioned above its a long commute etc and time to move on. No hard feelings or anything, just life!