If you can't get approved otherwise, it may help. It might also lower your APR, anecdotally they may base it off your mother's FICO score rather than yours, and that will likely be a non-trivial difference.
That said, as long as you have a sufficient downpayment, virtually anyone in America can get financed for an automobile if they're willing to suck up the APR associated with the loan.
Also I would also make the caveat whenever borrowing from family, make sure she gets paid back before anyone else... not worth the strain in the relationship to do otherwise if trouble strikes. End of the day, as long as the tradeline gets on your report, and you're making the payments, I think it may be a smart course of action though likely you would be able to do the two-step refinance anyway without much trouble assuming you don't have much in the way of auto history in the past.
Starting Score: EQ 561, TU 567, EX 599* (12/30/11, EX lender pull 12/29/11)Current Score: EQ 660, Wally TU 697, EX unknown (05/13/13)
Goal Score: 680 in all three (01/01/14)
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you have to put cosigner to be primary,and you will be cosigner. after 1 year try to get refinance to take the cosigner out, in the eye of lender,they make decision base on primary first,if primary not qualify for loan,they will have to look a cosigner, then if cosigner did not qualify then bye bye 
. on credit report. 3 CRA will report both of you guy. So the main thing is just get the Loan approval, thats it
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