Has she been checked out for food allergies as well? (gluten, casein, eggs, nuts... stuff like that?) Absent that, anxiety may be the culprit, in which case, some relaxation CDs could be just the ticket.
It's certainly worth a try, because they'll be good for her under any circumstances, and, diagnostically, they could be useful, because if they do stop the symptoms, then at least you know it's probably stress-related. (Please do have a look at this week's Inspiring Story too, which, oddly enough, also happens to be about a 7-year-old).
I would recommend Betty Mehling's Magic Island for her (one of the same recordings that helped Sam) as well as Charlotte Reznick's Discovering Your Special Place; Ready...Set...Release! by Jeffrey Allen and Roger Klein is another really good one. And of course Roxanne Daleo's work is fabulous, but it may be a little on the young side for her – hard to say – depends on the child.
Hope this helps. Please let me know!