Why does Dorothy want Kitty to come and stay with her and Charlie?

When Dorothy meets Kitty on the boat she implores her to stay with her and Charlie. She says she feels incredibly sorry for how she had misjudged Kitty. Before Kitty left for Mei-tan-fu, Dorothy thought her vulgar and frivolous. However, watching her bravely accompany Walter, Dorothy was impressed with her courage and bravery and wants to become friends with Kitty.