I also do not think your kids should spend a week with her. I also do not know if "confronting" her is a wise idea. She may have OCD or she may just be really particular but without your own medical training you can't really diagnose her or say she has a mental illness because she probably will not be receptive to that. I think you need to focus on her behavior regardless of an suspicions about mental illness. If you bring this up will she listen? Will she be receptive? It may be better to focus on what behavior is unacceptable to you and say something about that and leave the MI part out for now.