Many years has passed since her husband died.
It has been many years since her husband died.
Her husband has been dead for many years.
Her husband died many years ago.
どれもだいたい同じ意味になりますが、
その訳に合わせるなら、Many years has passed since her husband died. が適当かと思います
【訂正】yearsじゃなくてmonthsです…