I don't have a sister (always wanted one!), but I have a younger cousin and we are very similar. Personally, I didn't consider asking her - I didn't want to put her in the position of saying no, and of bigger importance to me was I wanted to have some distance - I wouldn't want her feeling like she was a "mom" to my child. I didn't want to look at my child and see my cousin. For me, it was just easier to let go of the genetic connection and pick an unknown donor that had a lot of qualities that I really valued. Everyone is different, and I hope you and your husband find the best option that's a perfect fit for both of you.