Darcy has always been unclear on why she was living in Stark Tower (or as some had taken to calling it Avengers Tower). Oh, she knows how it had happened. Darcy isn’t stupid or crazy. She clearly remembers and fully understands how she ended up living in the tower. What Darcy does not know is the reason she lived there, her purpose in the tower, in the household.
It has always been clear why each of the others is in the Tower.
Tony Stark is there because, well, he owns the place. The incredible Miss Virginia Potts (or Pepper as Darcy and most everyone else calls her) lives in the Tower because she runs Stark’s company and she was in a committed relationship with Tony Stark. Pepper is also wise enough to know that Tony cannot be trusted to stay out of trouble for long without her around. (Pepper is the only person to demonstrate a consistent ability to manage Tony Stark.)
Steve Rogers, Thor, Natasha Romanoff and Clint Barton each have a place in the Tower (when they are around) for various reasons, partly just because they are members of the team, The Avengers. Bruce Banner lives in the Tower as member of the Avengers, but also for access to the labs and workshops.
Even Jane Foster, Darcy’s best friend and sometimes boss, has a reason to be living in Stark Tower. Mr. Stark had invited Jane to move in as soon as he learned that she was an astrophysicist and more-or-less dating Thor. Apparently, Stark wanted another scientist to play with. Tony also kept a guest room available for Jane’s mentor, friend, co-worker, and unofficial godfather, Dr. Erik Selvig, who is sometimes around to work on a project with Jane, Tony and/or Bruce.
The others all have some special ability, knowledge or training. They’re scientists, engineers, executives, soldiers and agents. Darcy is just along for the ride. When Jane moved into Stark Tower, Darcy moved in too. Darcy still doesn’t know why the invitation included her but right from the beginning she set out to make herself useful. That’s why Darcy Lewis is now what she privately calls “The Science Nanny”.