Gas Expenses Reimbursed

My friend uses her car for work and submits her gas receipts to her employer who reimburses her completely. When my friend files her tax return, she uses her actual mileage and claims the maximum mileage amount that the the IRS allows.

It seems to me that she is not doing this correctly since most of the expense of operating her car (the gas) is really being paid for by her company. Is what she is doing legal?