Final answer:
Mallory should require a doctor's permission before performing microdermabrasion on a client taking blood thinners to prevent complications.
Step-by-step explanation:
If Mallory has a client who is taking blood thinners, it is essential that she requires the client to obtain doctor's permission before proceeding with a microdermabrasion treatment. Microdermabrasion is a skin procedure that may lead to increased bleeding, bruising, and other complications in clients on blood thinners. Ensuring that a medical professional assesses the risk and provides guidance not only prevents potential health issues but also aligns with best practice standards in aesthetics and skincare.