If she is an independent contractor, then your home is her place of work and she has no commuting miles. You do not have to claim deductions for a home office (even if you have one).
If your wife leaves home and goes to one or more of her clients' locations, the entire round trip is deductible since she was travelling specifically for business that she could not do at her own office (home). If she writes down her starting and finishing odometer readings, that would tell you exactly how many miles of her work day were deductible.
However, if she detours to stop by the grocery store or to pick up children from school, the miles she spent on the detour is NOT deductible.
If your wife receives a W-2 from any of her clients, the mileage to THAT location is NOT deductible since they are commuting miles.
Basically, if she gets a W-2, miles are NOT deductible; if she gets a 1098 or nothing from the client, all miles are deductible.