What is the ruling on not applying henna to my deceased maternal cousin's daughter, who died of cancer, based on her request, and what are the consequences of giving her a carbonated drink that worsened her condition, and what is the ruling on weeping over her?

We ask Allah to have mercy on your cousin and all deceased Muslims. There is no sin upon the family of the deceased for not fulfilling her request for henna or for not giving her a drink unless it contained a cure for her or was intended to cause harm, as this is what people usually do with their sick. It is permissible to weep for the dead with tears from the eyes and sadness in the heart only. However, wailing, screaming, and lamenting are among the major sins.