If she has a home office, that is considered her work place* and all mileage is deductible. Otherwise, her work place is where she physically works. But if she works more than one place in a day, the inbetween miles are deductible.
If you go to 2 or more job sites in a single day then the 2nd trip is deductible as an employee expense. For example you leave home drive 5 miles to the 1st job then drive 10 miles to the 2nd site. At the end of the day you drive 15 miles home. Only the 10 miles between jobs is deductible. The first trip in the morning, from home and the last trip at night back home are considered commuting and are not deductible.
*To deduct mileage, to the first client and home from the last client (normal commuting trips) the home just needs to be the "Principal Place of Business". It does NOT need to qualify for the Home Office deduction (the 'Regularly and Exclusively' rule does not apply). But, from your description, your home is not her Principal Place of Business.