Maybe just buy a Ring doorbell so if they take the TV out you have them on camera doing it/there's a monitor of what's going in or going out of the property.

Also, set up a ring doorbell camera at your front entrance.

Your burn rate is extremely critical and the reason why is because the amount of money that you spend daily to carry that asset or that home can eat away your profits so as an example if you factor in your monthly payment on interest, your utility bills, your internet bills if you're monitoring via camera if you factor in taxes and insurance HOA fees these are all things that add to your burn rate.

You can have a septic company run a camera down the line to check for collapses, tree roots, etc., but the coverage is relatively inexpensive relative to the potential cost of the fix.

She has been noticing things were misplaced in the home and set up some security cameras inside because she is single and traveling alone.  

For the last 20 years I have been in the home itegration industry designing and installing smart homes(home theater, security, cameras, computer networking, lighting control, etc.) as a project manager.

Has a gate, but I don't see any security cameras or systems on buildings. $50,000h. 

The video clip shows carpet that needs to be replaced (and hopefully not with carpet), a few (emphasis on few meaning not many) kids toys and possibly a closet door that is missing but the camera pans so fast it is hard to tell. 

If they vandalized the property, file a police report, set up cameras etc.   

Talk to the tenant and tell them that you are concerned there are people living there who are not on the lease and if that is the case, they are in violation of the lease and will need to move.Otherwise, put up a security camera, do inspections of the home, do drivebys to check for cars.