With my mortgage eating half of my income, it sounds crazy to take a second one. 

Work with a CPA to optimize your tax returns to reflect sufficient income for future loan approvals.

This can be a city or neighborhood.We manage a lot of Class C properties in the City of Detroit, so previous evictions are common.We typically do NOT allow within the last 3 years and we want to see stable employment, income and no other major credit issues since.For Class B rental we're looking for no evictions in last 5 years.Class A, would be at least 7 years.Of course, there are exceptions to all of the above for extenuating circumstances the applicant is willing to provide acceptable documentation for.

When she gets hit with a vacancy, she panics because she loses the income.

The purchase price vs rental income is very healthy (assuming occupancy and collections are there).

So you are negative $600 a month on the first one, you will need to have the personal income to cover it and then still buy the next one.A couple of thoughts:1.

I'll pass those even their credit scores are great and their income are 3x the rents. 

Build an emergency fund to cover unexpected costs, and ensure you can manage the mortgage without STR income if needed.

No matter the strategy so you can be ready in case anything happens where you lose your active income or a tenant moves out without notice whatever the case may be.

If the threshold were adjusted for inflation, it would be $3,037,840 as of 2022 and the $200,000 income would be $547,129.