Mary Morstan puts on her appearance like a mask, chopping her hair short and dying it with the cheapest brand she can find. She chooses too-bright lipsticks (too bright to look good with her new coloring, too bright for the situation) and applies her eye makeup in ways that aren’t quite fashionable. She goes to Oxfam and buys clothes that shorten her legs and widen her hips. If people are looking for her (and surely they are) they will look at her hair, look at her lipstick, and never look at her face.
She has always been excellent at distractions.