Most sensitivity issues are results of interractions. Do we know if the lady in question is taking anything else as well ?
Despite all that is known about Caffeine and other Xanthines, much isn't known.
However it is conclusive that people with generalised anxiety disorder are abnormally sensitive to caffeine. The effects are exaggerated.
I reference this...
Anxiogenic effects of caffeine in patients with anxiety disorders.
Bruce M, Scott N, Shine P, Lader M
Department of Psychiatry, Institute of Psychiatry, London, England.
As far as green tea goes, there is some theophylline in it. Not loads but some, and that also effects people differently.
I said a few things about theophylline in this post. In particular,
"theophyline has a narrow therapeutic range and high interindividual pharmacokinetic variability."