Dear New Wife,
I do agree with you that our children deserve to know and have a relationship with each other. I also believe that my daughter deserves to have a relationship with her father.
I realize that you probably won't believe me, but I have honestly never done anything to prevent dad from having a relationship with our child. In fact, until recently I had no idea where the two of you were even living.
Yes, I have kept in contact with grandmother and aunt, because I had contact information for them and because they were open to having a relationship with our child.
I cannot afford to come to Florida, but I would be open to ideas on how to give the children an opportunity to get to know each other.
I think that is as close to a perfect response as possible. Not argumentative or defensive. It doesn't mention the child support arears, and it gives the new wife some insight. Try it.