testing the waters with your friend is usually a great idea, as it will help you out. however, I have noticed the chritian youth a lot of times show the love of jesus(im Christian myself and am open about being trans and never cared much for what the elders thought) the Christian youth are usually unbigoted and have many times been the most vocal supporters of the transgender community where I live. (yay the 7 of us in my area are supported by peers alone) so, if your friend has had a proper learning of the bible, then he or she will be supportive and not hateful.
Love,
Lilly Garcia