Very good point about the arteries from the arms. Do you know what her blood pressure is when this happens?
Did the doctors happen to havest any arteries from your moms arms (ulnar artery) to use in the bypass? If so this could be the culprit but should be temporary. Is she taking statins? Statins can cause coldness and numbness in hands as well as anxiety attacks.
Please discuss your concerns with her cardiologist when she goes back for a check up, and he will be able to tell you if its just temporary. Good luck to you & your mother.