It's so nice of you to want to do this-- by all means, yes! Depending on your budget, get her a piece of jewelry -- the sorority has a catalog on their web site. Likely her sorority will give her a drop with the letters to wear with a necklace, but rings, bracelets, etc., would be something she could wear regularly and treasure.
Or... if you are not already paying for her dues, you could tell her you are paying all of spring dues, instead of a piece of jewelry. The amount of money will possibly be around the same amount.