My sister in law is a year younger then me, and we were best friends in high, and she introduced me to my husband, her older brother. We joked that the brother and I would marry and we could be sisters. Well, as things would have it, we fell in love and did get married. Right after, she got really mean and nasty. Of course, we tried to keep including her in activities, but she either turned us down or made everyone miserable.
Sometimes she's nice, usually when she wants something or is upset. She comes running back to us. However, at times she comes over and makes snide, passive aggressive remarks about my personal interests, my clothes, my height, weight, housekeeping skills and child rearing techniques. Granted, she has a rough home life, but her brother and I have always left our door open for her, and she knows that when she comes here there is a plate and bed for her. I feel like she's taking advantage of me. Why is she acting like this? We were best friends for years.