Here's what Texas says: https://www.txdmv.gov/motorists/buying-or-selling-a-vehicle/out-of-state-and-foreign-vehicles

So, if you have a proof of sale and your mother has signed off the title to you (which probably has to be notarized and she might be able to do this at her bank), you should be able to go to the Texas tax clerk's office within 30 days with your proof of insurance and Texas inspection, and have the title transferred to your name and get a plate. They'll process the title and return it to you if there is no lien on it, so make sure you have a receipt of sale, insurance in your name and inspection in your name. Your mother could also call her ins agent and find out if s/he could give you all more information, or call your own agent if you have auto insurance already.

The DMV site states the kinds of fees you'll entail.