Based on what you describe, I would get:
I think you mean Xanax? This is a sedative anxiolytic used, obviously, to treat anxiety
. It WILL NOT make her heart stop beating. It isn't a good long-term solution though because it is addictive and does not address the underlying problem. The vomiting
I can't explain or link to tachycardia- unless she is tachycardic because she is so dehydrated from vomiting. She may have an SVT
(a paroxysmal transient fast heart beat)- if so these are easily treated and carry a good prognosis.