It would help to know something more about the plant. Is it a woody plant? What sorts of leaves does it have? What is its habitat? Without that information it was difficult for me to feel that I had chosen plants that were similar to the one you found. However, below are a few suggestions for plants with lilac-colored flowers that are native to Webb County. Some of them are reported to have scents. For the others I could find no information about the scent. They range in size from about 1 foot to more than 5 feet. If you found your plant in a flower bed or lawn, it is very likely it is not native to North America and is an imported cultivated plant and, as such, won't appear in our Native Plant Database.
If your plant is one of these, the information about its attraction for butterflies and hummingbirds will be under the heading "Benefits". Observation will also tell you if butterflies are attracted to it.
If none of these is your plant and you have photos, please visit our Plant Identification page to find links to several Plant Identification forums that accept photos for identification.