Absolutely check it out. Colonies seek out a cross section of women on campus. They WANT women who are juniors and even seniors to provide leadership, diversity, balance and to prevent all of the women from graduating the same year. Having upperclass women also insures some alums from that chapter in the near future who will provide support.
Someone I know from my alumnae chapter was a founding member of her chapter and said it was an incredible experience. She was not a freshman .....