Help my EE hasn't laid a egg in several weeks.

We have a problem. My EE was laying on a regular basis, everyday or so until we introduced 4 new girls to the flock. Everything was fine while they were separated but as soon as we joined them together in the same run she stopped laying. It's now been about a month since her last egg. The other hens from the existing group have have been fine. The introduction and combining of flocks went surprising well except for this problem. Anyone have any suggestions?