How can i convince my good friend/ roommate to join a sorority with me??!!!?

freshman year she was all for joining one, but neither of us did. Now approaching our sophomore year, i really think that i want to go through recruitment and eventually pledge. I haven't brought my idea up to her yet because at the end of the year last year she claimed that a sorority is "just not for her". Even though i know she wants to, she just hates to follow in the footsteps of her older sister. we usually do everything together, so i know she will consider, but what is a good way to bring it up to her? i don't want her to think that i am trying to drift away from her.