raise?

Let me first start off by saying that I love my job. I really do. I actually enjoy coming to work and being there is never something that puts me in a bad mood.
Until today.
We've recently hired a new girl and she's totally fab. But I've learned that in addition to pretty much giving her my job and my hours, she is also being paid more. The bosses have said that they're trying to "be fair" in having us "share" the hours (which isn't fair at all in reality because she gets 3 times more hours than I do), but I'm really curious as to what the reasoning could be to pay her so much more? I have worked really hard for this store... coming in last minute when they've been in a jam, taken on as big of a load as I could (and getting it all done!) and pretty much have been an incredibly fab employee. So its no wonder that I'm really not happy about this...I feel I deserve some "fair" treatment here but I'm not sure how to go about asking for it....
Help!