Arngrim and Tracy were very close while filming on the set .
After the end of the series , Tracy maintained a friendship with his on - screen wife Alison Arngrim ( Nellie Oleson ) .
Alison Arngrim and Tracy were very close while filming on the set .
After the end of the series , Tracy maintained a friendship with his on - screen wife Alison Arngrim ( Nellie Oleson ) .