The only way to stop people like that is to go down the formal route and put in a written complaint to the PALS department re her attitude, lack of professionalism and the stress and anxiety she has caused you during this already stressful time. Explain what she said about the cancer patients and how it upset you. They have set procedures for formal complaints and it has to be dealt with. I will gaurantee she's nice as pie with you next time!
As for the tests, ring directly to your pre assessment suite and speak to the nurse in charge, explain the mess your Cons' sec has made and explain your anxieties, she will know the procedure and will ensure you are safe. Good luck chuck!