“How does a 5’5″ woman with a short torso appear to be longer and leaner?”
Create the optical illusion of a long, lean, vertical line through length and color.
Tops should hit her between her waistband and her hip to create length where there isn’t any in reality. If the top hits her at her waist band, she’s now created a horizontal line, cutting her body in half and thus, emphasizing her short torso. But, if the top extends further down and is a smooth, clean fabric, she’s created a longer, leaner torso.
Further, if she wants to tuck the top into her pants, a low-rise trouser is best for this. More of the shirt will show when tucked into a low-rise pant, again, creating the longer line.
Wear a longer top with a wrap feature or create a waist with a belt that hits at her high-waist (just under the bust line) or with empire seaming.
Lastly, (and easiest of the options) is to wear the same color from top to bottom. This alleviates any interruption between the top and the bottom; it starts at her neck and ends at her feet creating one, long line. A dress or a top/pants combination is the best wait to do this.