Just out of curiosity, I was wondering why you are getting it done? Is she getting really bad symptoms or not responding to meds? Here pH probes are generally only done when medications don't work or if they are having problems like Failure to Thrive. Is she on medication? If so, please check if you can get it done still, because it will make the results invalid. They should be off all reflux medications including mylanta (and some even say panadol) for at least a week, so it doesn't alter the results.