Also, I would be within my rights to get in there, change the locks and make sure she won't be able to break in again.My question is, do the police even enforce this?

Mostly Police/Fire owners, etc. 

What did the police say when they came?  

Your property shouldn't show up on Airbnb.com to the metro STR police because it will not fall into their date ranges.

Pretty much if police are brought to the property due to ANY police activity, if there are any charges laid they will be found in violation with the tennancy agreement. 

Tell them to file a police report.

If you want to really know what is going on in the city, join two Facebook groups - Portsmouth, VA Fire/Police Scanner and Portsmouth Political Pulse. 

Yep, out of my 33 evictions, I’ve had to PAY to evict 4 squatters and know right from the judges and police’s mouths - squatters have rights!

My time is WAY too valuable to deal with those types of problems.Chasing cashflow in bad markets is probably one of the main traps new investors fall into--read the forums and you'll find countless stories of new investors buying in C and D areas because "the cashflow was excellent", and within six months they're at their wits end with non-paying tenants, police getting called to the property, property damage, MIA property managers, etc., etc.

In the 1990s major cities began cleaning up their act by increasing effective police presence, aided by things like active cameras and debit cards, all leading to a decrease in violent crime.