Regarding the pulse rate change from 60 to 86-- that is not alarming in and of itself as it is still a normal heart rate.
Sometimes people with mitral valve experience experience intermittent palpitations and changes in the intensity of the murmur. I agree that an echo is a reasonable way to proceed.
The Doctor may say otherwise but this could just be an innocent episode. To be on the safe side I would schedule a simple echo test with your Doctor or local Cardiac Specialist to just make sure her valves are correctly functioning.
She's never been diagnosed with a murmur by either her internist or obgyn