Any Knowledgeable People on Texas Tenant Laws?

[Randy S.]

So, my sister is in kind of an odd situation and I'm not sure what she can do. Just a heads up, she didn't sign any lease agreement or documentation for anything (which she was already lectured), so I'm here strictly for advice on how to get a deposit back and I appreciate anyone for taking the time to read and reply to this.

Summary

-Sister was looking for a place to rent.
-Brother-in-law works with a landlord who had a vacant house for rent
-Verbal Agreement to move in on April 1st 2020 (No lease was signed)
-$1,200 Security deposit was given to Landlord (Without lease agreement or any documentation), paid through a money gram. Terms weren't really discussed besides monthly rent and move-in date.
-One week before move-in date, landlord is notified that my sister will not be moving in, so a verbal request for the security deposit is given.
-Landlord says "Brother-in-law" owes him money, so he isn't returning the security deposit. 

^I have no idea how someone can conclude this makes sense... but then again, neither does giving someone $1,200 with no documentation...

I'd appreciate any advice on how to help my sister get her money back.