Too many tenants try using bulbs that are not a match for the fixture, size wise and wattage wise, even when we have it in the rental agreement what is required.

[(Bulb wattage) X (3) X (Hours on per day) X (number of total days in her lease) / (1000)] X (the kw cost of electricity) In your letter, explain it is the past and future considerations for the hallway lights being fed from behind her electrical meter during the lease period and will be the only consideration made.

This would be a lot less expensive that a higher wattage heater. 

Next, determine the wattage used per hour for each device, and the estimated average daily hours of operation.

Generally, anything that creates heat is using a lot of wattage...curling irons, coffee pots, microwave oven, crock pots, etc.

I also don’t want to visit the property every month to note wattage usage.

I use all LED lights with low wattage in the hallways. 

They're lower wattage than a lot of these baseboard heaters, and I believe they are about half the watts used that a Cadet heater uses.  

I was looking into it, but the cost to set up panels that would actually provide me the wattage I need (about 11,000W per month) seemed prohibitive.

You might want to call a 'house meeting', get everyone on board to manage expectations then document after the meeting with addendum to your lease for increased utilities beyond an agreed wattage use.