She was 75 in 2012, but did not start taking distributions or roll the account over to an IRA for the four years she was retired?  

I had a similar situation with a client who had two IRA accounts but was taking RMD from only one.  This went on for four or five years.  We caught it before the 2021 return was filed so we filed the 5329 with it, and he withdrew the accumulated amount right away.  IRS has enough of a paperwork crisis, filing multiple 5329's might be technically correct but I wouldn't waste their time.  Maybe add a line to the one for the most recent year, "Taxpayer agrees to file additional forms for previous years if requested by IRS."  There's no statute of limitations on unfiled 5329's, right?  But there's no late-filing penalty for them either.  Or maybe there is, but if it's based on the amount of penalty owed, then it's zero if the penalty is abated.  And IRS always abates.