Is it really all that different than people having a baby shower for their second child? or third? Or for that matter any different than having a shower for a couple that has say, lived together for years. (in either case what could they possibly need gift wise?) I think that as long as she was honest about calling off the first wedding and returned the gifts ect. That there is no good reason to not have one this time around.
If it's really that big of a deal, make it a no gift party, or put something in the invites about gifts being optional and guests can call for registry info. rather than having people feel obligated to supply a gift. While the gifts from a shower are great, it isn't about the gifts, its about spending time with your friends and family and celebrating a major moment in your life. There is no reason that this shower shouldn't be special or that this wedding is any less special simply because she was almost married before.