So much about the STR, MTR or LTR approach comes down to your individual goals, possible pain points and preferred investing prescriptions.

You'll either need to acquire/reacquire prescriptive easement rights, negotiate a license or sue to quiet title if an abandoned claim. 

Part of the agent's role is to supervise to be sure that nothing bad happens, or to work to rectify it if it does.Either way, always advise the tenants well in advance (according to the terms of your lease) and tell them to secure all valuables (money, jewelry), prescription and weapons.I also recommend minimizing the intrusion on the tenants by scheduling group showings at specified times only. 

In all other respects, these dwelling units shall conform to the minimum prescriptive requirements for residential dwelling units.

The 24 month period mentioned is not a prescriptive regulation but is a "safe harbor" given by the IRS in Rev Proc 2008-16. 

The NFPA and the ICC developed and publish codes through a prescriptive process, mostly because some got hurt or destruction and devastation occurred.

However safe harbors are not prescriptive and there are others who think a year is OK. 

You are allowed to ask for proof of prescription.

If it were mine (and I don't do student rentals but from a property management point of view).Maybe coach the (young inexperienced) renter about calling several times about the same thing--ants, etc..Ask to see a copy of her class scheduled for this semester.Confront her directly about the suspected Narcotics issues and advise her on your (and the Police Departments) policy regarding that.Come at the issue with a customer service attitude vs. an adult/child attitude, ie.

There is a safe harbor (sort of) at 2 years with specific use requirements from the IRS but again the safe harbor is not meant to be prescriptive but only descriptive of one period that would be acceptable.Best advice - say your explanation to the mirror.