For the top of stairways, you can get battery operated, motion sensing lights that will come on in the dark - warning guests that they are getting close to a stairway. 

Also, you can get a wireless motion sensor security cam/monitor with phone app. and that you can actually talk into it.  

At this point, the power has been off for over a year and no attempts to manage the moisture (even with a regular dehumidifier) have taken place in atleast 3 years.

PM and myself feel, based on the description, that this mold was probably tenant caused and that we should show up to survey the process a bit and provide tenant with information about mold and airflow, as well as a dehumidifier, and have them sign an addendum to the lease that they are responsible for any reoccurrence of mold that they create via furniture placement etc.

That is to me the most important step, always in motion, never stagnant.

Light can also be a great disinfectant - a pole-mounted halogen and motion-activated exterior lights might be helpful.

It was a live-in slow-motion rehab, so we have made a lot of improvements in the two years we held.  

In the living room, I mounted my 50" tv on a very nice full motion wall mount.

Not complicated .. motion trigger flood lights

Time to give yourself a break, acknowledge that the lady is older and needs help (like our mom or grandma would), and now is time to be tactful, understanding, ethical and put things in motion to get yourself out of this one.