It seems that this leaves me open to liability for her to just be squatting there with the original tenants having moved out.

how could she use the toilet?  

Four units means 4 fridges, 4 stoves, four showers, four toilets.

When you are the bank you also do not deal with tenants, toilets termites etc...

Shouldn't be much to have a plumber scope the lines with a camera.The check toilets down then into the main line going out to the street.If it's septic they do a pack and die test to check for leaks going out to the tank in the yard.I don't know what the cost is to test a house.I figure a few hundred as when they do apartment buildings of 30 units and up it takes a couple of days and cost a few thousand.

In some ways you save - where you might not provide disposables through the entire stay (like toilet paper) but you'll want to have a fully furnished kitchen where I'm an STR you can kind of go on the lighter side on kitchen furnishing.

In a 300 unit apt community, I can hire a FT handyman that can go purchase 300 toilet handles (should be able to negotiate cheaper price per handle than w/SFR where I have to pay retail), the handyman is not charging me a per visit call and will know exactly why these flushers fail while an outside person at your SFR may fumble around, troubleshoot and not fix it right since its the first time visit to your property.But the other one is that commercial real estate is valued differently than SFRs and small MF (4 units and under) which are valued by comparables to other like properties.  

Your job then is to deposit the checks; leaky roofs and busted toilets are someone else's problem.

For someone that lives on site, we usually give them a small stipend (depending on the size of the property) for dealing with tenants and minor repairs, such as unclogging a toilet.

We had the tenant check the basement toilet which was dripping.I used a std commonwealth lease and just added things that specifically applied to my needs.