What is the ruling in Islam on a woman refusing to shake another woman's hand because she is wearing gloves?

A woman must wear gloves if her hand is adorned with henna, and it is impermissible to uncover the palms in the presence of non-mahram (definition) men. She may uncover them out of necessity or in the presence of women and her mahram relatives. Saying 'Assalamu Alaykum' (peace be upon you) is a Sunnah (definition), and returning the greeting is obligatory. It is a right of a Muslim due to its reward and its role in spreading love. Shaking hands is a Sunnah and carries great virtue in the forgiveness of sins and atonement for transgressions, and abandoning it means missing out on this reward.