How long do farmers have to keep their records

I am trying to buy a farm and have hit a brick wall, as need TVA paperwork and am being told that as she stopped farming three and a half years ago, she no longer has the records. Am I not right in thinking that records have to be kept for a minimum amount of years and if so how many years??

Her business was a company, does this change anything???

here are some basic guidelines, as far as tva is concerned according to this it's 10 years ;-)