Holding all else equal, your residential mortgage's interest rate will be 0.25% better, or about 1 discount point better (your choice).Currently, mortgage banks, brokers, and credit unions, are essentially run by compliance lawyers that earn more than they would/should, if not for the fact that a single alleged unproven infraction can easily be several million dollars in fines. 

Other than that, you could always send a lease infraction, unauthorized person living in property. 

Penalty is $11,000 per infraction.

So unless there are currently code infractions you shouldn't have to do additional work.

From my experience in city of Minneapolis, it's more than just a contact number the person of record, it's rather a big responsibility, the city would either call or contact if any infractions, or emergenciesTo be responsible in this nature you'd have to depend on the fact the person would actually respond.

TIL - When trying to obtain records for infractions/code violations for different cities in my area......... every place is different.

At one point, we carried the logic that of we kept tenants on month-to-month, we retained the ability to not renew them at any point due to lease infractions or poor behavior.

You'd get a lease infraction/violation notice more than likely prior to a eviction notice but anyone not on lease is an unauthorized person, so honestly surprised it's not been a issue yet. 

Just leave a note saying you entered to fix or service what was needed..if they won't let you in I guess you call water dept and have water shut off at the curb if it's water related.. call gas and have gas shut off at outside of bldg if it's gas related, notify police your building is unsecured and you have attempted to secure but have been barred access and need escort.. and you file eviction emergency action for cause I always have phone camera ready..the he said , she said on this will be a ongoing situation.. get them both out.. mutual lease termination if possible.. just document noise infractions,, and damages,, police calls are not infraction if they call themselves.. if neighbor call police get copy of report.. if you call its a unsubstantiated report/ shows bias and cant' be used as reason for eviction. better if tenant or neighbor calls.One way or the other they will get out.. damages will happen and better to safe guard yourself then to get between 2 crazy people.. the cops out there will tell you the most violent unpredictable calls are domestics.. and people get hurt, killed,, don't let it be you. 

You can ask current landlord for copy of her application, lease, any lease notices, infractions for past 2 years..And to verify her account is current.. if she owes landlord anything, it's not your problem but nice to know her account is current..