What if God Intended for My Child to Transition from a Girl to a Boy?

Questions about how to respond to someone who says that maybe God intended for her daughter to transition from a girl to a boy and how kids in a small youth group with a child who identifies as non-binary can navigate that situation with respect and allegiance to the Word of God.  

• How do I respond to my sister who says that God doesn’t make mistakes and maybe he chose for her daughter to be trans as a challenge for her to overcome (i.e., he intended for her daughter to transition from a girl to a boy)?
• How can my 10- and 12-year-olds, who are in a small youth group with a child who identifies as non-binary, navigate this situation with respect as well as allegiance to the Word of God?