I wouldn't have thought it would be too much more expensive and I'd recommend she does do it or the insurance company is almost certain to wriggle out of a claim if she has a problem on the way to or from a client.
I'm an accountant and have informed my insurer that I use my car for business as well in order to go to meet clients. They told me years ago that it added about �10 or something to the cost. Don't know about now. It was important to stress though that none of it was cold calling, as none would be for your daughter. Cold calling for salesmen etc is viewed as much riskier apparently.