Talk to your bros and see what they think. It's kind of neat that your fraternity is new to campus b/c the things you do now are going to establish the traditions that future generations of men in your chapter will follow!
There's no hard and fast "rule" or procedure you have to follow for this. If you want to give her a laveliere, give her a laveliere. Or give her the sweetheart pin. You're setting the standard for your chapter! I wouldn't present her with your actual fraternity pin until you are out of school or about to graduate.
Either way, she's going to love whatever token of the fraternity you present her with-- and she will also love the candle pass her sisters will honor her with
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