How can you go about reducing/mitigating those factors? 

That is something you really need to be careful on in what investments you choose and ensure you mitigate risks through proper due diligence, education in the investment strategy you choose, & proper team building to accomplish the goal.

Literally the 1st thing she should have done is move her stuff.The 1st thing a judge would bring (not that it should get that far) up is her responsibility to mitigate damages. 

Someone that mitigates risk for you through deferred maintenance and an extended average length of stay with their residents. 

Well, last I studied, measles, was essentially eradicated from the planet, via a little thing called A VACCINE... ...that is, until some really smart people decided to not provide the vaccine to their young children -which you know, worked really well, causing measles outbreaks, amongst those clever ones, to the extent we've not seen in 50 years.  

Today, I am going more in-depth on "Diversification" and will cover all the reasons subsequently.1) Diversification💥One of the biggest reasons investors diversify their real estate investment portfolio is to mitigate risk exposure.

I think I could 1031 each of the duplexes into a newer 2000s later build SFH in the 185-200k range and mitigate a lot of the vacancy/capex issues I’ve been having w the older duplex units.

:Unit count = 8-30 unitsLocation (Neighborhood Grade): B or C+ NeighborhoodYear built: Between 1960-2000 (Preferably 1980 or newer)ROI: 7% Cash on ROIRehab Scope Needed: A maximum of $9,000 Interior RehabOccupancy: 85% Occupancy (Minimum)Unit Mix: 1 Bedroom unit shouldn’t contribute to more than 50% of total unitsConclusively, sticking to your criteria mitigates the downsides!

If he's buying for the long-term (which he should be) then corrections should be inspected and will be mitigated over time. 

I have worked with my CPA to do as much as I can to mitigate capital gains taxes from the sale of one of our investment properties, because, after ton of 'spreadsheeting' various scenarios, even with a minor tax hit (ie not being able to/not wanting to use 1031 exchange from my house sale to roll into a TIC/DST/other 'like' asset) our capital will still outperform returns I would have had if just leaving it in this rental.