I am pretty sure she has the record as the First Lady who outlived her husband for the most years.
5th.
1. Sarah Polk 42, 1891 (based on years of death, so it could be 41 or 43)
2. Frances Cleveland 39, 1947
3. Lucretia Garfield 37, 1918
4. Edith Wilson 37, 1961
5. Lady Bird Johnson 34, 2007
6. Jaqueline Kennedy 31, 1994
7. Edith Roosevelt 29, 1948
8. Julia Tyler 27, 1889
9. Grace Coolidge 24, 1957
10. Anna Harrison 23, 1864
Mary Harrison, Benjamin Harrison's second wife outlived him by 47 years, but they were married after his presidency.
Lady Bird Johnson was the 2nd longest-lived First Lady after Bess Truman at 97.