Ok after digging around a little bit, it is interesting to find out that the FAA has a 1998 Aviation Medical Assistance Act.
I thought this article summed up nicely what the responsibilities are, and yes, flight attendants
are required to check credentials - and further,
can refuse the help if ID isn't shown.
This is from the Journal of Emergency Services (separated, for clarity):
http://www.jems.com/articles/2010/06/handling-flight-medical-emerge.html
"Despite these generous protections, EMS providers must continue to follow the standards expected of Good Samaritans.
EMTs and paramedics who choose to volunteer in an in-flight emergency may be required to show identification to the cabin crew indicating their level of training at the time of the emergency.
Air carriers may choose to refuse assistance if identification isn't provided.
EMS providers should only work within their scope of practice and not perform interventions or treatments they haven't been trained to do.
Whenever possible, an attempt should be made to contact the ground-based physician services the airline may utilize on a regular basis.
Based upon this, I am wondering a couple of things. One, was she able to produce her medical ID? And two, was the type of emergency it was consistent with her specialty of OB/GYN? These are two things I can think of that may have influenced the FAs decisions in going with the other provider.