Hi,
You might forward to her the document on this page (second one down). This is on the Pearson website, written by Pearson, and describes the use of the GAI. Perhaps she might be more amenable if she sees that it is a standard practice described by the test company themselves. It has a whole section on "when to use the GAI". You might draw her attention to that section. Sometimes a professional who would think they understand scoring better than a parent just needs to see something that feels official to them.
http://pearsonassessmentsupport.com/support/index.php?View=files&CategoryID=235
