There are far too many variables here to even begin. You really need to take your daughter back in to the doctor for a visit.
Does she vomit daily, or just a time or two a week?
An EKG & Echocardiogram
would be helpful to determine if there is any structural abnormalities with the heart. Excessive acid production can, and often will, cause some cardiac irritation, but would be UNLIKELY to cause weakness in the extremities unless the vomiting
is so significant and frequent that her electrolytes have gone out of balance. A blood chemistry panel will show this.
I agree, this DOES sound like a heart issue, and not JUST a GERD
thing. Get her in soon, and have them test her heart.