Well... you are right that it's disrespectful, but Rose might have loved Jack more than her husband! Besides, if she died she was almost right above the Titanic grave! So her soul( if she died) went to the nearest person she loved, Jack! I think she died! She kept Jack's promise too! she died an old lady warm in her bed, although she wasn't exactly in her bed, but she was in a bed and VERY OLD!!!!!! Jack made her promise that she would get married and have kids too! So maybe that's the only reason she got married! besides, no one could come in the way of their love and she couldn't love anyone else the way she loved Jack!