I know Jennifer know, Jennifer was named James originally, and I've known her since she was seven and I was nine. I should say, f'rinstance, 'back in high school, Jennifer and I were inseperable; double-dated a lot. She never used to wear trucker hats then.'
...this seems so damn obvious I'm frankly embarassed it wasn't my gut instinct.
One especially insightful suggestion I got on trans_advice was that one regard the transition as being comparable to the transition of Ms. Smith into Mrs. Jones: she hasn't become anybody else really, and it doesn't matter that Mrs. Jones was Ms. Smith when you and she first met. You'd still say 'Mrs. Jones and I were chums in high school' without referencing that she was Ms. Smith then, right?
Thanks for bearing with my '...buh?' on this, for helping me find the Miss Manners answer, and for your willingness to share your insights.