I think I understand your reaction. It is typical of Lydia's careless behaviour isn't it? Lydia and Kitty were apparently under the Forsters' care for the day yet I notice Aunt Phillips was present and lent the dress. Mrs Forster thought it a fine joke. Lydia and Kitty should know better but are allowed run wild with the officers. However, in the Forsters' home, Mrs Forster is responsible for their behaviour.If the reputations of Lydia and Kitty came to harm over this incident, Mrs Foster and Aunt Phillips as chaperones should be held responsible. To me that is where the real disgrace lies. It doesn't say much for Colonel Forster either.