The "she" can deduct vehicle expenses from "HER" SCH C. She has to file her own SCH C to do that, since she was an independent contractor for you.
I can tell you right now it's an absolute waste of time. There's no way her vehicle expenses would be enough to make any difference what-so-ever on your joint tax return. (Maybe a dollar if you're lucky). But since you paid her more than $400 as an independent contractor, she has to report it on SCH C and she must pay the additional self-employment tax on that income, in addition to any regular income tax that would be assessed.
