If you look at pretty much any information regarding how to respect a transgender person (many UK councils publish some - there are children as well as adults who are transgender, remember, all of it would cite not using the incorrect pronoun to describe a person in the past, because of the reason stated - many people have always thought of themselves as a certain gender, Nadia included, so it's pretty obvious.
Of course all transgender people are different. But it isn't a huge leap to understand why referring to a lady as he/him, etc to describe historical situations could be offensive, whether that's intended or not, as in your case.