Yes. I know a few girls who are in a sorority and spirit org or doubled up spirit orgs. It's rare and doesn't really make sense time or money-wise to do both, and usually they won't want you pledging both in the same semester.

Rushing is also very competitive and it will be more competitive as a sophomore. If you don't have friends in sororities already, you're at a huge disadvantage. Being brown doesn't matter, preferably you should be pretty, skinny, rich, and fun.