How to refer to future sister-in-law in ceremony program

My sister-in-law to be (my groom's sister-in-law) is going to be one of my bridesmaids. How do I refer to her in the ceremony program? As Sister-in-Law of Groom, Sister-in-Law of Bride, Friend of Bride?? We are close and she is like a sister... I could always go with Soon-to-be Sister-in-law of Bride for humor purposes but it is too long... Thanks!