You mentioned something about the sorority having the mission to help integrate freshmen into college-life. Just a note...many organizations and schools restrict sorority membership to women who have earned at least 12 credits (so they would be pledging as second semester freshmen at the earliest).
My sorority (which is multicultural) has environmentalism as a secondary cause (primary is breast cancer)...but individual chapters can participate in their own causes as well (as long as they contribute to the national causes as well). More information can be found on our website.
Best of luck to you!