How Do I properly adjust old Balance Sheet balances?

I just took on a client who has books that are a MESS. There are several accounts on the balance sheet that are obsolete- lines of credit that have been paid for over 2 years, payroll liabilities that had been sitting there since 2015 when she switched to full service, old credit card balances, a vehicle purchased in 2012 and more. Normally I would try to track down what happened and record everything appropriately but I'm lost, here. This could take a lifetime! She has multiple bank accounts that she went through and have since closed so tracking it all down is really not a practical solution. I'm wondering what is the right way to handle this? How do I make these adjustments so they will make sense to the tax accountants and not upset them? Thanks Pardon typos, typed using hand held device.