Dollar. Store. Everything. Seriously. Do candles in your letters, decorate picture frames. Also I don't know if your campus does this but for our big/little decorations every day has a theme and you can really have fun with them. For ours' the last day is always Sigma day (and your 'family' day so my family is the Winnie the Pooh family so we always give Sigma and Pooh related stuff). But the first two days I've done Penn State day (so gifts centering around the theme of Penn State, so PSU homecoming shirts, white out shirts for a football game, dance maraTHON shirts, blue and white anything) and favorites day (which is super easy to customize to everything your little likes--i.e. favorite food, drink, music, movie, etc). This could definitely cut down on the amount of Chi Omega stuff that you would need.
You could also quickly make some letters with fabric and puffy paint. Or even press on letters (though they should really be stitched ASAP to keep them together). You could also do this on a plain tote bag. Another thing I did was make a tie blanket (directions can be found
here) in our sorority's colors for my little, that was pretty easy and was a useful gift too. Also remember that you can decorate things (like mugs, cups, frames, headbands) to make them Chi O themed. Also things in your colors are also great. Balloons and streamers can also have a really 'wow' effect without much cost. Do you have a crafty sister that can help out? I was always recruited to streamer and decorate and puffy paint. Use your resources!
If all else fails though, write her an IOU. That's what I had to do with my first little because we got matched the semester after I initiated and I had literally one shirt to give her. So instead of getting them all that day I just bought her every shirt that we got for the next semester and gave them to her that way. It will work out. Remember, as a little you're going to love your big no matter what. Looking back my big did not really get me much stuff (and wasn't really the most creative) but I was just so thrilled that I was getting anything that I was blown away. And remember, your relationship will (and should) supersede the things you get her (although they're nice). Best of luck! Let us know what you decide to do!
Edited to add: Michael's/AC Moore's dollar section is also your best friend. I know for my other little I managed to find little pens and papers with her initials on them, purple and white travel coffee mugs, and also wooden letters that she could display in her room. You could also paint the letters cardinal and straw colored. Also magazines, candy, snacks, coloring books, and crayons are all fun presents that I know I'd love.