I think you did the right thing in that her life was being threatened by the building owner. I would just be extra dilligent and keep an eye out for "lost cat" posters anywhere - phone poles, laundromats, area stores - any place people might post it, and in the local paper. You could also post a "found cat" flyer, but don't give her description, just "Maine Coon found by 43 Main St. office" or a vague-at-best description, so if someone calls, you can ask for them to describe her color, size, etc., so you know it's their cat.

At least she's safe for now, and you can be happy about that!