Ask Mr. Smarty Plants

Mr Smarty Plants thinks the LBJ Wildflower Center has a great design resource that you should add to your tools.  In the "Expore Plants" topic of the webpage is a link named Recommended Species.  If you follow that, there is a link for Native Plants for the Texas High Plains, and also, farther down the page, all of Texas by Ecoregion.

You didn't say exactly where your clients area was [because we have slightly different lists for "High Plains" and "Rolling Plains"] but I expect it is in or near Lubbock, so I used the High Plains Ecoregion list; we can further limit the search by sorting for "Full Sun" and "Shrub".

That returned a list of 5 candidates, ones that are very resilient to your weather and which gives you a bit of choice as to configuration.  Why don't you consider these? [pictures below]:

Verbena halei (Slender verbena)                1-3 Ft.

Acacia angustissima (Prairie acacia)         1-4 Ft.

Amorpha fruticosa (Indigo bush)                6-10 Ft.

Rhus aromatica (Fragrant sumac)            6-12 Ft.

Cercocarpus montanus (Alderleaf mountain mahogany)     8-20 Ft.

  I looked a little bit into the Salvia texana (Texas sage) that your client said did not do well.  In its plant record it states that Salvia texana is a denizen of limestone soils from north-central Texas south to northern Mexico.  This means that it is likely not well adapted to the weather and soil near Lubbock, so it would need extra care to thrive.  If you have a plant that you would like to recommend for an area, perhaps you should look at the USDA distribution maps.  A link to that is in the Plant Record on the line that says:  

USDA Symbol: SATE3

Hope that helps!     Mr Smarty Plants