According to the school's website first semester freshmen are not permitted to pledge a sorority. There will be rush events the second semester where you will meet all the sororities. This is formal rush - you cannot only meet one sorority. This enables you to keep an open mind and look at all the sororities to see which is right for you.
Even if you're an upperclassman, it might not be good to contact the chapter directly - it can be seen as too bold or forward. Keep an eye out in the fall, the chapter will likely post signs announcing whether or not they are taking new members. If they are at total they will not be able to take anyone during informal rush in the fall.
http://www.stmarytx.edu/greek/display.php?go=rec