As I understand it, Elenwen isn't essential after the CW and/or MQ anyway. I will check someday on the one character that has completed both and/or on the 2nd one after I complete the MQ and if I do the CW.

I know I can get into the embassy after DIplomatic Immunity, but Elenwen wasn't there at that time.

I went in soon after finishing the CW, with the MQ I had gotten as far as Alduin's Wall and finding out about Dragonrend but I had yet to go back to the Greybeards and ask them about it. Pretty sure she was still essential as she kept taking a knee and then getting up again. I reloaded and marked her as mortal before going in the second time.
When we went to the Embassy I picked the lock on the front gate, killed everyone outside, picked the lock on the barracks and took care of the ones in there, then used the console to open the front door. Elenwen was still in the main front room where the party was held in Diplomatic Immunity. The waitress from the party and the drunk guy who can cause the distraction for you were still there as well. For some reason I did not go in that room at all on the last PC where I went back to clean out the Embassy after the CW. I had finished the MQ on that character though so maybe anyone who is still in it just disappears from the game once you finish the MQ? I don't know. There were still Thalmor outside the Embassy and in the barracks and one wizard back in the building over the dungeon, though.
From there I had to unlock several doors with the console to get to the back part of the main building, from there out into the courtyard and rear building where the private quarters and dungeon are with no need to resort to console. Nobody was in the Solar, I just went in there to do some extended looting. A lot of their silver and one bottle of Colovian brandy are now in the master bedroom at the Palace in Windhelm.
