I have to agree... you have to make the choice that is right for you. If she's really your friend, she'll remain your friend regardless of what happens during rush.
My two freshman-year roommates and I made an informal pact that we'd all try to get into the same sorority. Only one of us actually did. I dropped out of rush to join a local... looking back, I'm glad I did, because if I'd joined the sorority we all had in mind, I would have been miserable. My other roommate attended pref parties for that sorority and one other - she was so wowed by the other sorority's pref party that she listed it first on her pref card. So we wound up in 3 different sororities but were still friends.
