Breaking this up into 3 parts: essential details, additional details, and questions. Read as much or little as you want.

Essential details:
-shy, conservatie girl who has at least been somewhat interested in me
-A lot of other fraternities on campus were having big parties that a few of my friends and I were going to check out. Around 11:00, right before we went out, I texted her "A few of us are checking out the parties going on. If you and anyone else want to tag along, let me know"
-I never heard back from her until she texted me at 2:30 "Dang I just saw this..I'm at Fiji with some sisters.  Are you still out?"
-I never responded because everything was dying down by that point.

Additional details:
-At one of the houses we went to, I saw her across the room with some of her friends. We didn't make eye contact, but I know that she had to have seen me. We weren't there long, and I didn't go up to her because this was before she texted me back. Honestly I was kind of annoyed that I hadn't heard back at the time and was trying to freeze her a little and make her question my interet level.
-My roommate's fraternity is having a big party that I am going to tonight. I could definitely invite her to come with me if I wanted to.

Questions:
-Did I do the right thing by not texting her back and not approaching her at that one party?
-Do you think she actually didn't see my text until 2:30? (I know this one is more pure speculation)
-Advice on how to proceed from here?

Not really enough information for me give you a read. I think this is WAY too early to be asking for reads. It sounds like you guys haven't done anything, at all...

Not responding was fine. If you don't have a point, or didn't know of some amazing party that she just absolutely had to go to, I'd say texting back would have been the wrong thing to do.

As far as the text, anythings possible, and she may or may not have seen the text. But here's what's important - it's completely irrelevant whether she did or didn't to you. Don't worry about those details.

No idea where to go from here, I'll let the pro's give you advice on that, but use caution, this seems like a big friend zone trap to me.