Thanks for your short comment !
I hope that your overall impression of the apartment and your stay in Paris was good.This was what I felt when we meet the 30 April 2018 at the apartment.
There is a security code for the first door and then you need a key for the second door in order to enter the building. I am note sure how the homeless woman got into the building and unfortunately, this could happen in many buildings in all large cities over the world.
As soon as you informed us that there was a stranger in the staircase, I came to the apartment and when we asked her to leave, she went away immediately.
I do understand the situation was uncomfortable for you and your family, however, I am glad we could resolve it quickly.
I would not consider the building of this apartment as a "dangerous building".
It is located in the very city center and there are always a lot of people around (residents and turisits).