What is the ruling on a wife's feeling of shame for not sitting in mixed gatherings where she adheres to her niqab in front of her relatives, and for shaking hands with non-mahram men? And is this considered blameworthy shyness that reaches the degree of disbelief?

When the family gathers and non-mahram (definition) individuals are present, the gatherings of men should be separate from the gatherings of women. If men and women gather, then the woman must cover her body from non-mahram men. It is not permissible for her to shake hands with a strange man out of shyness from people, for this is not disbelief as long as she has not deemed unlawful acts permissible. However, she must abide by the limits of Allah and not allow shyness to prevent her from enjoining good and forbidding evil with wisdom and good counsel.