Start with a gentle, secure feel
A good sheepskin slipper should feel gently held at first, not loose. Natural wool has loft, and that plush layer will settle slightly as the slipper is worn.
If the slipper feels roomy on day one, it may feel less secure after the wool relaxes.
Choose the shape for the way she moves
Open-back slippers are easiest for slow mornings, reading, and moving around the bedroom or kitchen.
Closed-heel slippers add a steadier fit for stairs, longer wear, and anyone who wants more hold around the foot.
Leave room for comfort, not sliding
The toes should not feel pressed, but the foot should not slide forward with every step.
For customers between sizes, the better choice depends on whether she prefers a snug natural-wool feel or more room for thicker socks.