There are few pieces in the winter wardrobe that do quite as much work as the long sleeved shirt. These must-have staples provide structure under layered looks and can also anchor standout statement ... Hence, there is no ambiguity with the men, and for the same reason no ambiguity with the ladies.

Understanding the Context

Ladies is the plural form of lady, so the apostrophe goes to the right - ladies'. If you are wondering why we don't write ladies's, it is because ladies is one of the exceptions, along with girls', parents', players', weeks' and even Klingons'