What should I do about this the office manager where I work made a mistake & now I have to pay the IRS?

$1000 when I file my income tax. Because on January 1, 2012 she (Jessica) didn't update the income tax chart and used the 2011 chart Not realizing that as of January 1, 2012 the taxes went up. So she didn't deduct enough taxes from my paycheck and when my accountant did my income taxes for the year 2012 he told me that I underpaid my taxes and when I file my 2012 taxes I have to pay the IRS $1000. When I mentioned this to Jessica she said she used the tax charts from 2011 since the difference was only a few dollars a week. Those few dollars she neglected to deduct added up to $1000 Which I have to pay now.