I'd install a programmable thermostat - assuming it's a central air unit.  

Maybe a smart thermostat or something.Do not let tenants dictate your upgrades - they sound like a PIA, honestly.

I would hire a qualified PM to manage the property, it can be a pain with college students, i have had some pretty good ones in mine so far. ( note: check agreement with PM usually they charge a leasing fee to you, lets say $300 for each lease agreement, group of 3 students is one lease, 3 individual students is 3 leases or $900, make sure you have in your agreement that if they get a group it can be 300 but if its an individual maybe 125, this prevents them from getting single students and costing you a fortune.)3. definitely have them get renters insurance and make sure your PM has that on the lease agreements.4. in PA you can charge 1 1/2 months security deposit, i know my PM charges 1 month5. do not know of any in Erie, sorry6. rent should be based on the area and your PM will know better on that. my Student rentals, i include heat( sometimes you can set a limit and then have them pay the overage), sewer/ water, garbage, lawn maintenance/ snow removal and internet. they pay for Electric ( stove, dryer and hot water heater are electric.) i include the internet because it helps rent them and i can control the thermostat on all of them and front door lock on one of them.you are just finishing up your reno now, but if you invest in another student rental, use 5/8" drywall on the walls, harder for them to damage, plus gives you better fire protection.

Maybe some startup types that are ok if their programmers don't have windows?

I asked her to change the filters and double check the thermostats (there's independent upstairs and downstairs controls) and get back to me if it's not better.But how would you all proceed??

I'm a retired programmer and know the IRS has programmed algorithm triggering of high risk returns based on the numbers and tactics found from a computer scanning basis. 

She's paying heat/hot water for the entire building at the cost of $6,000+ per year, although each unit has its own thermostat.

(Note:  the thermostat was in a locked box set at 69 degrees in a different apartment.)I asked him why the window was open when it was 20 degrees outside. 

We do have to charge money for the service since we do not make money when a property is sold, and the monthly cost of programmers to run the site is over $20,000.4.

As a web programmer dealing with security, privacy and ID theft, I've learned to NEVER post a personal picture to any website, not Facebook, Twitter, here or otherwise.