For what ever reason I can't seem to see the pics, brands are a tricky thing in Texas because of the county to county registration.
My first suggestion is to contact the person you bought the horse from, and ask if he has a bill of sale from when he bought her, and see if there is any info there.
If you are very, very, lucky he has a brand transfer, that will make it all easier.
However, I am afraid that what you are in for is a long and probably frustrating search going from county brand book to county brand book, luckily they are all online because that's 254 counties worth of brands.
I would suggest starting in the county you bought the horse in and work your way out, most sales tend to be within 150 miles or so