Is a reclusive girl who doesn't speak much with her female relatives when they visit, sinful for not having an intellectual connection or for fear of pretense and self-abasement?

You bear no sin for not elaborating in conversation with your female relatives, as this does not constitute cutting off ties of kinship. We advise you to ease your mind regarding this matter, for your conversations with your female relatives—even if they involve some effort—do not humble yourself. The matter will become easier if you seek Allah's help and train yourself to interact with people and converse with them within the bounds of Islamic law and benefit.