I believe "henceforth" is closer to "dorénavant", in that it's higher in linguistic register.
I have asked before for people to explain when they have used the term "linguistic register" since I had no idea what is. I had received no replies to date.
For myself and others, I looked up a definition: " "Linguistic register” refers to the concept of adapting one’s use of language to conform to standards or traditions in a given professional or social situation". All it means is adapt your language to the situation in which you find yourself.
So, lemmingofdestiny is saying "henceforth" is a word typically used in a professional or technical communication rather than in casual conversation.
"She is now closed" doesn't make sense. "She is now closed off" does, and I got it wrong with that.
I think "she" in this case could refer to "la porte" or some other feminine noun and not necessarily a person.
In English, people only use personal pronouns for objects they have a lot of affection for. More likely "she" is a car, not a door. It is worth noting that the more likely translation is "it", not "she".