Could very well be a reaction to something negative going on at home. As severe as abuse to as simple as mom now goes to the gym once a week and a babysitter has to put her to bed. Is the parent aware that you are having the issues and does she use them at home.

In daycare consider setting up a play yard or sectioning off an area and putting safe toys in there and that is where she stays. She may join the group when you are directly supervising/interacting but at first hint of an issues she goes back alone. She may just be becoming sensitive to someone in her personal space.