Based on what you said, I see no red flag, but verify her husbands income. 

@Corey GilroyTo reclarify, just checking other listings for permit numbers is one way to check if there may be permit regulation.Obviously reach out to the local zoning department, county auditor, and county permitting department for the most accurate route.

I called the city planning and zoning department with questions about regulations, and they were super helpful.

My plan is to convert the R-4 (residential zoning to CG or commercial general).  

People on here say it's a red flag.

But winter - stay far far away.I'm not into STRs at all, but that seems another red flag to me.

When looking for an STR make sure that the area will provide a unique experience to any guests that may be staying there (Business trips, Amusements, etc).On top of that, make sure that the area has high rental rates, and that the area's zoning rules are not restrictive towards investors.

I am doing some research on Tax Increment Financing zones in Waco.

Along with the possibility of 2 units, for example one in main bedroom, one in open livingroom area.... it's also worth considering 2-zone (or more than 2 zone) units that have one outdoor unit feeding (via copper lines under home) multiple indoor units that can be controlled independently.  

St Tammany is a pain in the *** when it comes to anything that involves planning and zoning's approval.