--don't feel guilty. Without your advocacy, Billye would never have been accepted as a patient at Mayo. (Her doctors certainly weren't going to push for it.)
I understand the feeling that it would suck if Billye goes through all this and there is no further progress on diagnosis or treatment, but you did a good thing. (A mitzvah.)
I do hope that the Mayo people are conscientious enough to send her all the testing results/clinical impressions without a lot of pressured asking--and, IF something definitive is found, to follow up with her physicians regarding therapeutic or other recommendations.
(We may all want to gear up to flood her physicians with IVIg evidence.

)