The primary goal of 99% of students after graduation is to find a job! My husband was given his first job ONLY because he was Greek. (His 2.5 GPA sure didn't help out.) The supervisor said that he looked specifically for Greeks because they had leadership skills, time management skills, and - very important to this company - social skills. NOT partying, just the ability to strike up a conversation with a stranger and sell something, which is basically what Recruitment is!
A good friend was given a job because of her Greek experience. Another friend who does a lot of hiring for a major pharmaceutical company gives preference to applicants with Greek affiliation.
Not to mention, as someone did above, the connections and contacts that you will have. Perhaps your interviewer will wear the same letters. Once you graduate, join the closest Alumnae Association and I would almost guarantee you come out with 10 business cards and opportunities for employment.
There is so much else that everyone else has covered. I ditto it enthusiastically. I was worried that my parents might object, and since I was living at home, it might have been difficult. They supported my decision as they knew it would broaden my horizons. I met my very best friends through Alpha Delta Pi - including my husband. I could not possibly imagine how my life would be if I hadn't joined!
Good luck! Your mother loves you and only wants to protect you. Once she realizes that GLOs are not about parties, they are about sisterhood, service, leadership, and so so much more, she'll come around!
