You will still likely see continue to see the discoloration after its dried.  

A real fireplace like that will discolor from either smoke or heat after a while. 

Even after scrubbing the brick was just discolored.

I am adding ceiling insulation to the whole building to remedy the discoloration problem on the ceilings where the insulation has blown away from the attic vents.

Purchase a cheap moisture meter and see what the moisture content is on the dis-colored areas and compare to the non dis-colored areas.I have had this problem before when the tenant did not run the AC (trying to save on electric bill) and when buying a house that had beed closed up for a long period of time.Do not use bleach.  

There are warps in several areas and the siding is discolored.

@Sheree Hsu If you're pulling permits for the rehab then code enforcement should not be a problem, but I would not go there unless you have to.I would remediate (not test) the mildew or discoloring in her unit and evict her asap.   

By the time the insurance gott involved it was causing water damage to the interior of the home and was starting to get discolored (we don't use the "M" word in our office.)

The discolored portion is in a semicircle and is maybe an inch to two inches wide is the countertop usable?

After soaking for 5-10 minutes, we would use it to get paint out of carpet, off linoleum, etc with no discoloration.