Disclaimer: I worked as software engineer for a CRM device company.

From what I learned during my medical training, this king of issue is not so uncommon, but it is usually diagnosed very easily. Her peacemaker can be disabled using a simple magnet. This is a common test in nearly all protocol to check how the heart is working without the help of the device. Doing this simple test while upside-down would have shown that the paecemaker was effectively working in that position. That should have be enough to ring a bell to most of the cardiologists.