It is agony to be a hypochondriac It is not much fun being someone whose illness wasn't diagnosed until too late to cure it, because the tests were missed out to spare them a bit of worry.
If your friend has been sent for a colonoscopy, it is because what she has reported to the GP, or what he has observed, could indicate that something is wrong. She was anxious enough about her health to consult him/her. Now she is receiving tests to see what is wrong or whether it is "just" anxiety, and if necessary treatment can start. She could have stayed away from the doc and gone on worrying, but that would not have resolved anything.
Are you beefing about the GP for doing his job, or about her for being too quick to think she is ill?