UPDATE: I more closely examined the birth records of Kirsten's children, and I found a witness, Maren, from Skyum in one record. I believe this is Maren Christensdatter who is a confirmed daughter of Christen Michelsen and most likely Kirsten's sister. I also found another witness: Mads Knackergaard of Skyum, who is the husband of Anne Christensdatter another confirmed daughter of Christen Michelsen, and most likely Kirsten's other sister. I don't know why there is no birth record for Kirsten in Skyum in 1740 - perhaps it got omitted from the records? I suppose that can happen.