Stress causes the release of hormones that increase pain perception, such as cortisol and adrenocorticotropic (ACTH). Stress hormones also cause muscle tension. The back and neck muscles are particularly more sensitive to the effects of stress.
Without proper attention, a vicious cycle of stress and pain can easily be started: Stress causes back muscle tension, leading to pain, which in turn increases muscle tension and can further increase stress.
Maybe test her theory of being allergic to cats or maybe even some of the scents or something from her friends house. She should also consult a doctor to be sure.
