How about yoga, and cycling for that matter. To me there is nothing like a good hard ride to get a lot of stress out of my system. You can follow it with some soothing yoga stretches. Or if you are having trouble to sleep, try a hot bath followed by some calming yoga stretches before bed, stuff like that.

Or, if there is real stuff stressing you, try to deal with the real stuff, one problem at a time, assuming of course that they are things you have control over and can make changes that would allow you to feel less stressed. If they are things you don't have control over, like your nieces illness, then all I can think of is physical activity, yoga, good books, etc.