"she is claiming one room at her residence for business."

That needs to be its Exclusive use. It cannot be a home office that includes paying personal bills and doing personal tasks, or a shared space.

"but I am still confused"

What you have now described is found in Pub 587: "Principal Place of Business"

A lot of people think that if they are "in business" that makes all use of their vehicle a business write off, but the locations and trips have to qualify. The work being done at home needs to be principally done at home; that means is this salon work, admin work, or both. You have to determine if the Home Office is the only place this work is being performed, or not. Example:

"To qualify to deduct the expenses for the business use of your home under the principal place of business test, your home must be your principal place of business for that trade or business."

The person likely has office space at one or both business locations, so is the home office Principal Admin Office for tax purposes? It's likely not going to qualify as salon space, since there are two business locations for that activity.

Or,

The person is a hair stylist and sees clients in both business locations, such as Mon-Wed-Fri in Location A and Tue-Thurs-Sat in Location B. That means all of this is commuting.

Or,

The person goes to Location A in the morning, then to Location B from Location A in the afternoon, and then home from Location B. That means home-to-Location A is commuting and Location B-to-home is commuting. The trips between the two locations are business miles, as would be supply runs.

What the person uses the Home Office for, what this person does at the business locations, and what is provided at the locations, helps determine if any of the trips from Home to any location, or location to Home, is other than commuting.

Good luck.