If you're one of the lucky ones who enjoys a good relationship with your sister-in-law, you will find that there are many benefits of having her on your side. Your mother- and sister-in-law likely know your spouse better than any other women. A sister-in-law can be very helpful in giving your spouse advice and putting things into perspective by offering an outside opinion. A good sister-in-law will also be a loving aunt for your children, someone who can help you when you need a sitter or have a family emergency. Investing your time and energy in developing a good relationship with her will result in many positive benefits in your family life.

If your sister-in-law and your spouse didn't have the best relationship growing up, chances are this will be reflected in how she treats your family. The way siblings related in their childhood will greatly affect the kind of relationships they have as adults, explains therapist Jill Cedar in her Psych Central article "What Role Do Sibling Struggles Play in Adult Relationships?" The insecurities and resentments that she felt toward your spouse during childhood can keep her from being able to develop a healthy relationship with your family. She might still feel that she is in constant competition or has to prove herself as she did during childhood. Understanding where her feelings are coming from is the first step in trying to build a cordial relationship.

It can be hard on a sibling when the other sibling finds a partner and gets married. If she seems resentful, it may be because she doesn't spend as much time with her sibling as she used to. She might feel she has been supplanted in some sense by you. To try and smooth things over with this kind of sister-in-law, make it a point to include her in family activities and to encourage your spouse to take time to spend quality time with her.

If your spouse's sister is accustomed to being very involved and having a big influence in her sibling's life, she will assume that she can continue doing, so even after he or she is married. overbearing sisters-in-law tend to be overly involved with your family. Although they mean well, it can be stressful to have someone always telling you what to do. The best way to deal with this kind of person is to learn to say no. You should learn to not let your feelings be controlled by these pushy people, and to learn to say "no" with confidence, advises psychiatrist Mark Banschick in his Psychology Today article "Adult Bullies."