To dream of your sister-in-law, denotes to features she has and those you find within your own personality. It is also very important the relationships you have with her in your waking life, as it could tell much more about a dream. If you have a great friendship with your sister-in-law, then you have good qualities within yourself and the ones you like in her.
Dream dictionary: sister-in-law dream meanings
It indicates that family structure will be changed.