It is a dry campus because it is a Christian university. My roommate came back and told me she was drunk and to not take anything she said seriously. Then she told me not to tell anyone she was drunk. Should I tell my RA anyway? I don't know what to do
Having some fun is ok, but is unfair for your roommate to put you in this situation. She is endangering your school career as well as her own. She is also putting a lot more at risk than she realizes, and for this reason, you must give her an ultimatum.
When she is sober, take her aside and tell her that the next time it happens, you will report her to your RA. If it does happen again, do what you said that you would do, and report her to the RA. The punishment your roommate will receive will be much less than than other evils that could befall her, and you will be able to live with a clear conscience.