Which part of Texas do you llve in? My late husband was from East Texas where it is very humid, summer or winter Your mother probably is not accustomed to high humidity as, at any temperature, the moisture in the air will make it seem colder. Also, if you have moderate to high winds, that will make temperatures seem much colder.
When my family visited Texas in the winter we were dressed as "Hanucks of the NOrth"!, but we weren't cold.
In summer time, when we visited Texas, or any part of the south eastern U. S. the high temperatures, coupled with high humidity made us wilt.
Here is a tip to help alleviate the cold feelings: Wear dry clothing. If you have been outside, and doing any kind of physical activity, you will probably perspire. Change your clothes immediately as that will help to warm up.