Relationship expert, author, and divorce blogger Kimberly Pryor answers: It is possible to remain friends with your ex-in-laws if both sides want to maintain the friendship. I suggest asking your former sister-in-law to lunch and over the salad or appetizers let her know her friendship would mean a lot to you. If she accepted the lunch invitation to begin with, she's probably receptive to the idea.
Be careful to never say anything bad about her brother in front of her. And I would also recommend not spending more than a second talking about what's happening in your ex-husband's life. The idea is to break away from him. If your former sister-in-law is always updating you about his dates and other activities, he'll still be occupying a place in your mind and it will be harder to let go completely.
Kimberly Pryor is a journalist and the author of The Indestructible Relationship, which won the EPIC eBook Award for best nonfiction of 2012. Visit her blog at www.afterdivorceadvice.com.