Karen Foster, 52, admitted four counts of theft and four of false accounting totalling £550,000.
Ipswich Crown Court was told that Foster, of Andrews Walk, Bury St Edmunds, took cash payments from EMG Motor Group in Fornham Road between 2004 and 2012 and kept them after recording them as debts.
In December 2012, though, Foster gave herself up to police after dealership officials’ suspicions were raised.
She was being paid approximately £8 an hour for her work and making repayments on a Jaguar and Range Rover.
In mitigation, Foster’s defence counsel said that it wasn’t clear why the missing money had gone unnoticed for so long.
Another court hearing will be held in June, when an application to seize assets from her will be made so that they can be used towards compensation for the dealership.