TSCI Time Frame

Have a friend with a current DOD Secret clearance that was completed in late 2020 or early 2021. She had a Department of Defense Secret Clearance from 2011-2013. She has been offered a DOE position which requires a “Q” clearance, the DOE equivalent to a DOD TS clearance. She had some potential tax issues in 2006 which have never came up in any background check and she has never heard a peep from the IRS about. It is my understanding that the TS process goes back 10 years on residence, criminal investigation and credit but can go back to your 18th birthday on tax issues. Is this the case?