Is it permissible to punish a sister who is late in repaying her debt by visiting her for only one hour without the family and offering only gifts, in order to make her feel her negligence and responsibility?

Your sister must pay the debt she owes you, and her procrastination is an injustice. You can present the matter to those who have influence over her. As for visiting her without your children, with the aim of admonishing her, it is permissible if you believe that it will be beneficial; otherwise, it might lead to a rupture of ties, which is forbidden. Be careful not to demand payment from her if she is in financial difficulty; rather, grant her respite until she finds ease.