Mozar, doesn't your mom do her appointment setting and/or book/record-keeping for the appointments inside of her office? If so, then she is using her home office substantially and regularly to qualify for the home office deduction. I've used TurboTax schedule C and don't recall it asking me to differentiate between how much of the work I do outside the home office vs inside of it, but since I set all my appointments in my home office, as well as my preparation inside the office, while conducting the work outside, I deduct the entire home office, which is a certain percentage of my house. I also take record my mileage.
If your mother wants to make it simpler, she can always just take the simplified home deduction rate, which is something like $5 a sq ft, limited to 300 sq feet? This way, there is no need to depreciate property. This is usually a lesser amount than the standard deduction method, but it might not make a big difference depending on how much she makes.
But yes, take both deductions.