From my experience, if a helper stay in your home for more than 4 years, she would get into an unstable condition. I don't know the actual cause of such problem. It may be a side-effect from the aging DNA. Or it is the result of the long term battles between the employers, the respectable seniors, and the helpers. Human relationships can't last very long nowadays, especially the relationship between employers and employees (helpers), I think. Originally, I planned to use my helper for many many years. Indeed, she has been here for more than n years. But after tonight's battle, I think I would revise my original plan. This is the 2nd time I seriously consider whether to extend her contract in last 3 years.